Multiple lines or extensions on Mitel phones?

I’m trying to get familiar with some new (to me) Mitel 5224s. In the Key Programming area, there are line keys – Lines 1 through 4.

In short, I’m wondering what the line keys are. Can I have a different account associated with each key, so Line 1 is Ext 201, Line 2 is Ext 202, and so on?

What I would like to do is associate a particular DID or extension to each line, so phone calls to 555-5555 go to Line 1 and calls to 666-6666 go to Line 2. Conversely, I’d like my outgoing calls from Line 1 to show the appropriate caller ID, and the same for Line 2.

I guess I’m just not real sure what these lines are for in the first place or how to use them.

Any info would be appreciated! I’ve been Googling around, but I can’t seem to find any good info on these.