Each type, pelistal, thelodica, nuimqol and nian, has a specific set of items it gives research for. Their own bots, weapons and other things that tie more lossely into their faction. Industry bots, and perhaps some other "universal" things come from any kernal.
rank 1s max out at standard mods
rank 2 max out at t2
etc
rank 5 give a bonus to research. (not certain how much)
Research happens in a linear fashion, whereby you have to have learned the previous tech before learning higher. Can't learn to make a seth before you can make an Artemis for instance.
Light and assault give light tech
Mech Kernals give Medium Tech
Stop researching when you
a) finish researching what you need from that type or
b) get a message saying you have learned all you can from that type of kernal.