Howdy Jill,
I would love to help you as best I can here.
It sounds like you must be using WooCommerce. One thing I should make clear is that Event Tickets Plus is basically just a small addon to WooCommerce. Acceptings payments, processing orders, all of these are part of WooCommerce itself and have nothing to do with our plugin. As such when you are trying to find help and tutorials for these things, they will commonly be found on the WooCommerce website.
Simplify Commerce and Stripe are both “Payment Gateways”. Most folks end up using Stripe. Here is a great tutorial that walks you through what a Payment Gateway is in WooCommerce. If you are after an easy answer, I’d just use Stripe. But if you’re interested in researching this and finding out which one is best for your business, I’d start with an article like that one.
Once you have chosen a Payment Gateway, checkout the WooCommerce documentation for setting it up. For instance here is how to setup Stripe’s Payment Gateway.
Is that starting to make more sense now? Does that answer your questions?
Cheers!
– Brook