You put them in the Logos Manipulator to create Actions you can actually use. It's possible to put in just 1, 2 or 3 and the results are always fixed so if you know what to make (either you remember a combination or checked online) then that will get you your actions. You'll be able to combine up to 6 later on though trying to mix more than 3 will start to offer a chance of it failing and you'll lose any Logograms you used for the process, but you might also get dual actions so you have to decide if it's worth the risk or not.

I think most of that is correct, anyone else can add to it if anything is missing.