If you have a local git repository (with commits) and you want to push it to a Github/Gitlab (etc) repository, this guide will help you.

Git global setup

git config --global user.name "example example"
git config --global user.email "example@fastmail.com"

Create a new repository

git clone https://gitlab.com/youruser/yourrepo.git
cd yourrepo
touch README.md
git add README.md
git commit -m "add README"
git push -u origin master

Push an existing folder

cd existing_folder
git init
git remote add origin https://gitlab.com/youruser/yourrepo.git
git add .
git commit -m "Initial commit"
git push -u origin master

Push an existing Git repository

cd existing_repo
git remote rename origin old-origin
git remote add origin https://gitlab.com/youruser/yourrepo.git
git push -u origin --all
git push -u origin --tags