As Jonathan.Brink has pointed, it depends on the OS you are using.
But frankly independent from the OS it consist of the following 4 parts.
Yes, you have to first create a bin folder in your home directory. You could use either a File Manager or terminal. Google prefer terminal.
mkdir ~/bin
Secondly you should put the bin directory in your PATH.
PATH=~/bin:$PATH
This is like saying "In this directory I have put some special code. Treat it as an application"
Then you have to download the actual repo application. You could either use curl command as google suggest
curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
or this url. If you download the file on your own, you should put it in the bin directory you have created.
The file is a python script. So you have to give it permission to execute. To do so you have to use the terminal again:
chmod a+x ~/bin/repo
If you have any questions, I'll be happy to answer them :)
P.S.: If you are using Windows, you could use following discussed a post already