The first thing to do is look at the kit itself and see what communications capabilities are built into it, and how you can use them - this probably means a look at the manufacturer's site and / or their technical support. There isn't necessarily a "common specification" for serial comms and unless you can program the machine itself directly (unlikely but possible) you will have to work within whatever framework they provide. Most manufactures provide documentation (but the quality can leave a lot to be desired!)
Once you know what data you have to send / receive and how to do it the PC side should be relatively simple, if you are familiar with serial comms already. This should help a lot:
Serial Comms in C# for Beginners[
^] - Glen is an electronics engineer who also does coding, and it covers it all pretty well with examples.