How to do unity collaboration with one of my friend

When ever i watch YouTube videos it nwver seems to work and collaborate can any please help me in telling me how tp do it

Use GIT for version control. Version control is a must even if you are working alone, it serves as a backup and lets you see the history of changes in your project, so you can easily explore and revert specific changes done in the past (for example, when fixing a bug you unknowingly introduced in the past). Having a remote GIT repository, hosted for example for free on GitHub or your own server lets you share and merge these changes done by multiple people at the same time.