Can I "poof" items or DC's on my LD?

It's certainly possible, but it's much easier to do otherwise.

Also, I see how you're a "noob". Would you like to join a lucid dreaming discord that I can help you at?

Sure, the only reason anything at all would be hard is if you think it'd be hard. So if you have it in your head that that would be hard, than maybe it would be but here's a tip.

If it's hard to make yourself believe that you can poof someone into existence, just look at the ground and think "when I look up they'll be there" and then they should be.

It'll be easier to believe it'll happen because, since you weren't looking, hey, maybe they just walked into the room on their own, whatever.

Absolutely! You can literally create whatever you want in a dream. Your thoughts and your beliefs are your creative tools. Go into your next dreaming knowing that and watch things appear before your eyes :)