What you need to make the connection between controller and battery? that's a difficult question to answer because we don't know what tools and parts you already have. We do have extensive documentation showing how to make an electrical connection between a controller and battery such as our battery documentation page
The installation section covers how to make a connection via a couple different methods, there are other ways to do it of course including soldering or even just using wire nuts if you are just bench testing it. Additionally there may be differences depending on what model sondors you have, we cannot make guarantees about a product that we don't sell since they could make a revision and not tell us about it. But assuming everything else is all good and you have the controller and the display, then yes all you need to do is wire up the controller to the battery in a safe and reliable manner and using XT 90 is probably the choice you want, but it's up to you to determine how you want to go about actually making that connection. Typically with large wires, the easiest thing to do would be to crimp it using heat shrink butt splices. You would need the splices for this as well as a crimper and a lighter to seal the heat shrink after it is crimped.