I am trying to push code into Github using command,
git push -u origin master But it is asking for username and password and when I enter username and password it is giving error as "remote: Invalid username or password." 
My username is "saekhan". I tried this with saekhan, "saekhan", @saekhan and "@saekhan". Please tell me where am I doing wrong?
One possibility is that your password includes a special character.
Then you should need to percent encode it (see "Percent-encoding reserved characters")
Check also your git config credential.helper: with a recent Git, it should ask your credentials through a popup window to cache them in the Windows Credential Manager
git config credential.helper Make sure you are using the latest Git for Windows.
I see a https://github.com/saekhan/node-course-2-web-server, so make sure your remote url is set to that repo:
git remote add origin https://github.com/saekhan/node-course-2-web-server # or git remote set-url https://github.com/saekhan/node-course-2-web-server 
To be sure, you have read/write permissions to repository.
Check remote server:
git remote -v At Git source code folder (at same level at where you seen hidden folder named .git)
git config user.name "YourFullName" git config user.email "[email protected]" then retry.
git remote get-url origin?