There are two approaches to sending an email with attachments. The first is to share one or more items using an app that created or manages them and the second is to compose an email in the Mail app and attach one or more items.
Here is how to send an attachment starting with an app that created or manages the items you wish to share.
Apps that can be used to share items as email attachments include Pages, Files and Photos. In the documents view of Pages, or in the Files or Photos app, browse the folder or album from which you want to share and locate and double tap the select button near top right. (In some apps, you may need to double tap on a More button to reveal the select button.) Now select one or more items by double tapping them.
Next locate the share button near bottom left and double tap.
A share sheet will pop up at the bottom of the screen. The share sheet includes many sharing options. Slide your finger to locate the Mail button which will probably be near the centre of the bottom of the screen.
Double tap and a Mail compose screen will appear. The item or items that were selected will be attached to the email. Complete and send the email as usual.
The second approach to sending attachments begins with the compose button of the Mail app. Compose an email in the usual way. When you have finished writing the message body you can add your attachments.
A toolbar is positioned above the keyboard when you are editing the message body. Slide a finger above the top right of the keyeboard and you should find the Insert Drawing button. Slide your finger to the left to locate the Insert Attachment Actions button and double tap. This pops up a menu. Swipe right if necessary to locate Attach File or Photo Library as required. Photo Library lets you select multiple items from your recent photos but Attach File allows only one file to be selected. I've recommended sliding a finger to locate the Attachment Actions button befause swiping left and right through the toolbar may not be available on your device.
Finally, send the message as usual.
The toolbar will also be available when you are replying to an email.
Note that if a document has been created in apps which use their own formats, such as Pages, Numbers or Keynote, you may need to export the document into a different format for it to be easily accessible to all recipients. PDF is often the most appropriate choice unless the recipient needs to be able to edit the document.