create or move to seprate branch with git checkout -b branch_name & git checkout branch_name
make and push your changes with git add . or git add -A
commit your changes with git commit -m"commit msg"
pull or fetch from git on that branch with git pull origin branch_name
resolve the conflicts if occurs
push your code to github git push -u origin branch_name\
Note that it is recommended to check status time to time with git status