These are some basic steps to get the code from your Git Repository and push the updated code.
1) Clone code available on your git account to local or dev. git clone <url of your repository>
eg: git clone https:\\github.com\<user>\<repo>
It will take some time , depends on the size of code and your internet speed.
If you already have clone code with you , but need to update your code with the git hub code
you can use
git pull <url of your repository>
2) You can check your repo branch Using.
This is an optional step to just check your are working in which branch of repository.
3) Modify Your Code.
4) Check the modifications using:
This will tell you the modification done by you.
5) Now , you can add those modifications for commit , using
git add <file or directory modified or newly added>
if some file or directory is to remove
git rm <file or directory name>
6) git commit
This will commit your code into your repo.
When you issue this command it will ask for your git username and password , if you are authorized to push the data it will push your data