How to handle changes on files on git source control before pull last changes?

There are many ways to fix it.
Option 1 :

A. Do local stash save :> git stash save
B. Then do :> git pull origin whaterver-remote-branch-name
C. then merge local changes :> git stash pop

D. Resolve conflicts if any, and then test your changes local, so that you are good for commit and nothing else is broken/erased.

Once you are done with test, sometimes simple visible test will do too.
E. Add your changes :> git add . or git add filenames

Push to same branch :: ideally you shouldn't do this look "Or" part
F.Add commit comment :> git commit -m "meaningful comment so you know what have changed now, make sure that you mention merged content"
G.Push your changes :> git push origin whaterver-remote-branch-name

Or push changes to remote branch
F'.create new branch :> git checkout -b feature/your-changes-to-remote-branch
G'.Add commit comment :> git commit -m "meaningful comment so you know what have changed now, make sure that you mention merged content"
H'.Push your changes :> git push origin feature/your-changes-to-remote-branch
I'. Create Pull Request
Option 2 :
Skip stashing, do git pull, then resolve conflict, then proceed with push.
Step B, D, E, F or B, D, E, F', G', H', I'

Option 3 :
Commit your changes to new branch and then create PR to master/origin branch.
E, F' G', H', I'