Git Page

clone the project on your machine (git clone "project")

pull devel branch (git pull origin devel)

branch to devel1 (or any other name you wish) (git branch devel1 then git checkout devel1)

make changes

check changes (git status)

commit devel1 (git add -A & git commit -m "commit message")

rebase (update) local devel (git pull origin devel)

merge devel1 on devel (git merge devel1 devel) 

eventually resolve conflicts

push to devel online (git push origin devel)

you can delete the branch devel1(git branch -d devel1)

You want to make new modifications: create a new branch from your local devel (git branch devel2 then git checkout devel2)