How to add members to code?

I have been coding an app but didn’t know how to add other people to come join the project and code with you. Like if you’re making an app with multiple people how do you all collaborate on one file at one time?
Thank you

Using version control (Git)

What do you mean?

Before collaborating on code with someone. You should look into what is Git and how to use it.

From there you can share code on GitHub and work on a project together