Very important question for many users at this point.
If you have purchased a new M1 chip Mac, then you will need to change a small setting in your Terminal App, so you can still run 'brew' and apps that are comming from 'brew'.
Go to the Applications folder and next to the Utilities folder.
Right click on the Terminal app, chose 'Get info'
and then tick the 'Open using Rosetta'
Now when you start the Terminal app, you will be able to install brew and run all commands.