I just went ahead and read this:

https://www.planetminecraft.com/blog/how-to-earn-experience-points-on-pmc-452402/

Gave me all the info I needed, plus just posting all over the forum gives some experience and recieving emeralds too

If you go to your profile and hover over your avatar/banner, you'll see a little Edit button; click it, go to "Profile" and you can change your class. The class is the "Network" bit you have currently set. "New" is the rank that level 1-5 users have. You unlock a newer rank and more classes as you gain XP.

XP is gained by contributing to the site; posting submissions, getting emeralds on the forums, etc etc.

You gain more XP by posting project on Planet Minecraft. And new Network is your rank, which mean that you are new here.