I'm rather new j
Here, how do I purchase more coin?

You can't purchase them, you can earn gold by playing quests, doing battles, selling pets you've caught/bred and you will discover more ways when playing more.

Hi :) I'm newish too. Gold is hard at the beginning but its so much easier if you do missions. I was really struggling until a couple of players helped me figure that out.
https://www.sylestia.com/explore/town/?town=esiorshaven/#town then click on "Town Barracks"

I've been using my two battle pets to do the first two easiest missions. Those ones don't fail so much so I always get 800 gold and 4 mission satchels every hour that way. It adds up pretty fast. I was able to get 20k for a new stable tab in just a couple days that way.

You might have to unlock them by following the first battle quests. I can't remember now.