I've jumped ship from Discord, like many others, I have questions!

I'm pleased to be here! I have searched this sub and still have some questions. I'll cut to the chase:

1. I created a server. How do I make it invite only?
2. I created channels on that server. How do I make specific text channels private, and only visible to select users on my server?

Sorry if these have ben answered already, hopefully your answers will also help others with their migration from Discord.