Assume that you have an empty repository in GitHub and no project starter anywhere

1. Open a local project
2. Clone a repository into the local device (can use GitHub Desktop to do it)
3. in Spring Tool Suite, Git perspective click on add an existing local Git Repository to this view
4. Select the local repository that you have cloned earlier
5. Pull
6. Go the the Java Perspective
7. Right click on the project -> Team->share project
8. Select the repository added to the view earlier
9. make changes
10. select unstaged changes and add to staged changes
11. write commit message
12. commit and push

Assume that your teammates have created some project starter for you

1. Clone a repository into the local device (can use GitHub Desktop to do it)
2. in Spring Tool Suite, Git perspective click on add an existing local Git Repository to this view
3. Select the local repository that you have cloned earlier
4. Pull
5. right click project in the Git Explorer ->Import Maven project

Once you make some changes to the code and want to upload:

1. commit as many times as you want
2. push/push upstream, if there is an error, pull then push/push upstream