Planning to start a business, need help with payment solutions.

Hi, I'm into agri and have got almost all sort of organic vegetables in our farm. We've been so far selling it in local Sunday markets and is quite happy with it. Recently, couple of guys who do the same, but in organic raw food items mostly, came to me and asked if am interested in starting a shop with them, of organic food. It felt interesting and along with few more guys we are planning to start as a shopping mart. As of now the business is only setting up, and while, Versapay (Tor) checking the payment option, it was tiring. So many options and so many technicality.
Went through an website relating to payment solutions, and some of the technical terms like payment solution, payport, payment gateway etc came by, what exactly are they??