When using computers there are many different places your data can end up, be that somewhere in your personal storage [like the local 'Downloads' folder on your equipment] or more likely in an online storage facility. Here it may be a filing mechanism [like Google Drive] or buried away in a web server operated by a service provider. The latter could either be a business with your personal details, or something less formal associated with an account you hold, like for example your Gmail at Google, but either way the 'data' held in the Cloud this way is usually very safe and only accessible by you.
As a quick reference you will find a list below of a selection of different types of data you already use, and where they are held.
For more information, and to refresh your memory, take a look at the second slide presentation on the Home page called "The Cloud" vs "Local"
Bookmarks : These are little bits of information that are stored in your browser, and synchronised online. They contain URLs [Uniform Resource Locators] that are basically pointers to web resources like your favourite websites. See this Wikipedia page for more information.
Cookies : Again these are little bits of information that are stored in your browser but you never actually get to see them - their purpose is to improve your browsing experience by holding pieces of information [so you don't need to re-input each time you visit a given site, and also to speed up access in general. See this Wikipedia page that explains their use in greater detail.
Downloads : As the name suggests these are 'files' that you have encountered either on the web somewhere or as an email attachment - in both cases you initiate the 'Download' by clicking an option. When you decide to 'Download' a file [say a PDF, or a photo etc.] to your 'Downloads' folder then it becomes your responsibility to look after it, and it may be moved it to another 'local' folder or just delete when finished. If it came to you via email [and you have saved that email in a folder] then it will be available online until such time as you delete it. If it was obtained using a download facility from a website then you can always go back and download another copy if you need it, providing of course that the owner of the website has not removed it. See this Wikipedia page that explains their use in greater detail.
eMails : These are stored in the Cloud, under your email account, and read by either a web service [like Gmail that accesses them directly] or through a mail client [like a Gmail App on your smartphone that copies down the entire email for you to access locally on the device] in both cases everything like synchronisation and back ups are done automatically for you. However although a high proportion of emails are just read and discarded there will be many cases where you want to retain them for a period of time for reference. In this case it would not take long for your 'Inbox' to fill up and unmanageable. This is where you make use of folders within your email account to create a 'filing cabinet approach' to store and emails you want to save. You might set up folders for things like 'Car' or 'Garden' or 'Finance' or any other meaningful name you like. When you move emails into these folders it helps to keep your Inbox nice and tidy, and where smartphone Apps are being used all of these changes are automatically sychronised to your account so that no matter how you access the email service you will always be presented with the same view.
Smartphone Storage : As mentioned elsewhere you can use Apps on your phone to manage different kinds of data. There are basically three different circumstances surrounding your data. [1] data is held on your device only [2] data held locally on device and synchronised to the Cloud [3] data that is held in the Cloud, without a local copy on your device, where you use the App to access / manipulate it on a website / web service. Obviously type [2] and [3] look after themselves, but if you have any data that is type [1] then you need to make sure you look after it. For example this could be a free standing camera app that stores everything locally - in such a case you could take steps to manually synchronise the photo files it creates with Google Photo's or Google Drive, or any other 3rd party service you may choose.
Sound & Video : Managing these files is basically no different to looking after the other file types mentioned above. In most cases you can 'stream' the films or music ''on demand' from a number of services like Youtube, Netflix, Spotify etc.Generally speaking the service provider will look after everything for you but if you get a file [say a video clip from a friend] then you may want to save it somewhere to play later. In such cases you will need to take manual actions as explained above.
Web Storage : This is the name given to web servers / services to which you have access for storing 'files' or various types. There are many such services [some free, some paid for] the choice is yours. If however you opt for a free service like 'Drive' that is associated with your Google Account then it may be the only service you require as the free allocation of space if generous and if you do need more you can purchased extra capacity, or maybe just get yourself another free account with something like 'Dropbox'. See this Wikipedia page that explain more about the workings.
Here are some online storage sites where you can open a free account. You can then back-up personal data and easily share nominated pieces with other individuals.
Account holders get a generous allowance of 'free space' from these companies but if you find that you require more capacity then it can usually be purchased for a small monthly premium.
Evernote - is available as an Android App, for smartphone or tablet, and also as add-on for your browser. You can use it to store information at their site [including typed or clipped information you send to it by e-mail] and it can even read text appearing in photographs so that is searchable too. It's worth taking a look at their introductory video. Support Page and click here for site status and other information
Google Drive - is a key component of Google Workspace and provides all Google Account holders with as generous amount of storage with integrated tools.
Keep Contacts [formerly known as Everdroid] is a great companion App for Evernote users that backs up your smartphone and lets you manage settings etc. via a user friendly web interface.
Pocket - is available as an Android App
Pushbullet - is available as an Android App, for smartphone or tablet, and also as add-on for your Chrome / Chromium browser. Either method gives you access to your registered devices and nominated friends so that you can 'push' messages with text, links, lists and photo's. Click here for a feature overview
To-Do Manager from Microsoft - is available as an Android App , an Apple App, or directly online.