The Finder is your access to all the files on your computer. The Finder dates from the 1984 Macintosh, where it was its landmark feature. After going through a complete redesign in 2001, the Finder we know today has remained mostly unchanged since 2003. Let's take a look.
Finder: Apple
This is a summary of all the files on your computer (go figure). Here, I've sorted mine by type, and then date opened, using this button.
and then
This holds your favourite folders. You can put a folder here by dragging it in, or using Finder > Preferences in the menu bar.
This is your Home Folder. It holds all of your things. If you have more than one user account on your computer, each one gets their own home folder so as not to get in each others' way.
It is recommended that you do not store anything in here, but rather, use this as a way to get to other folders.
The Documents folder, inside the Home folder, is probably where you'll be spending most of your time.
It is recommended that you store documents here, the same way you'd store pictures in the Pictures folder, videos in the Movies folder, etc.
You can create empty folders or folders with files in them. To make an empty folder, choose File > New Folder in the menu bar, or control-click and select New Folder.
To make a new folder of some files or folders, select them, control-click, and choose New Folder With Selection...
Click once and press Enter/Return on the keyboard. Type a new name, and press Enter again.
To move something, simply pick it up with the mouse and drag it to its new spot. Drag-and-drop is very common on the Mac. If you hover over a folder without dropping (letting go) the folder will "spring" open so you can see what's inside and keep dragging down more.
Copying
Highlight it, and press ⌘+C (that is, hold Command and C at the same time) on the keyboard. Click where you want it to go, and press ⌘+V.
See https://help.apple.com/machelp/mac/10.12/index.html?localePath=en.lproj#/mchlp2605 and Organize files in folders for more info. See also: Get Info.