You need to add your files and push them to your repository.
git add -A
git commit -m 'first commit'
git remote add origin git@gitlab.domain.com:username/repository.git
git push -u origin master
Step by step:
Add all files in repository
git add -a
Commit files (with commit message 'first commit')
git commit -m 'first commit'
add your remote gitlab repository(git@gitlab.domain.com:username/repository.git) as origin
git remote add origin git@gitlab.domain.com:username/repository.git
push your files to origin
git push -u origin master
Hope this helps?