If I buy something or anything off the marketplace and use it I my game, do I need to have permission from the creator to use it? Or once u buy it, it’s mine to use however?
Once you bought it, it’s yours to use however you like in your Unreal Engine 4 projects. 
The primary restrictions are a) you can’t re-sell the content pack itself to the Marketplace or to another site, and b) it’s only for use in the Unreal Engine.
Here’s a link to the terms if you’d like more detail: https://www.unrealengine.com/marketplace/marketplace-business-terms-faq
As far as I know in the terms you linked it’s not written that it’s only for use in Unreal Engine 4. Stuff that is sold in the marketplace is allowed to be use anywhere, but the demo stuff from Epic which is also “sold” in the marketplace for free is only allowed for use in UE4.
Below the Project name there is either written “Licensed for use only with UE4 products” or it’s not written there… And it’s only written below Epic official assets.