I have tried navigating around discord and cannot figure it out. I got an invite once to a pretty chill page but cannot find my way back to it now. Can anyone give me some advice on how to find some open active chats on there?

I use discord in the browser only.
If you got an invite and join the room/server an icon on the left column appear. Each room/server have his icon. A list of the content of a room/server is displayed in the column to the right of it .

Is there a way to search for open rooms....or do you have to receive an invite to a room?

You always need a currently valid link to join.
You can search them with google. For example: search with "discord jobros" and one of the first hits is an invite from a site called dishboard.org.
Sometimes you can find links on reddit.
When u join the room, u have to accecpt the rules for access.
In the rooms mostly u find links to other rooms. Or you can
ask another people.