For real world trading, do you mean the FM (Free Market)? When I just started playing, I picked up all the crap I can, and sold them. You can just try farming in places where high meso drops (try searching up a meso farming guide).
For party quests, you just make a party and do whatever you're supposed to.
Zakum in particular, you might want to search it up, as it isn't easy for someone who is new to MapleStory (just like me xD).
The Zakum PQ will require you to make some kinda sacrafice item, which you can just buy it in the FM.
I keep rage-quitting in the jump quest since I'm so bad at them xD
Good luck!