I have a question about the word "je" and the suffix "-um."

I'm learning through Kurso de Esperanto and lernu.net, mainly, and I'm learning those two words. But in the way it describes them, its more or less a word and suffix, respectively, with no specific meaning.

I'm afraid I don't understand and I can't find anything to help me out. Can someone explain a little more in depth?

The suffix -um is undefined, but it is useful to think of it as meaning "doing the thing implied by the root".

For example, "Butiko" means "store or shop". What do you do in stores? "Butikumi" means "to go shopping" (i.e., the thing that you normally do with stores).

That's about the best I can do. It really is a kind of vague thing. What's really happened in a lot of cases is that particular meanings have been assigned to particular -um words for various historical reasons that seem kind of arbitrary now, but whatever... now those are the accepted meanings, and you just have to memorize them, since there's not much rhyme or reason to them. I've seen some -um words whose dictionary meanings left me scratching my head as to why exactly THAT meaning was chosen and not some other one.

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"Je" is the preposition you use when no other preposition will do.

For example, imagine watching a show on television. What does the "on" mean in that sentence? The show isn't "on top of" the tv (which is what "on" really means). It's sort of "in" the tv, but really that's not truly accurate either ("in" the tv are a bunch of electronics and wires and whatnot).

Shows are actually "emitted from the screen embedded in the front of" the tv. But there's no preposition which means that, AND it's not even really important to the meaning of the sentence. All we want to do is indicate that the show and the tv are linked together, but we don't care how. So here we would use "je". It functions as a preposition structurally. It says "gramatically, a preposition belongs here, but none of the actual prepositions I can use would be literally true".

It's amazing how many prepositions in English aren't used for their meanings, but as just sort of linking tools, independent of their literal meanings. Like the "on" in my example. It doesn't really mean "on". It just links the show to the tv. English picked "on" for some historical reason, but there's no reason some other preposition couldn't have been chosen that wouldn't have worked just as well. That's because the meaning of the preposition, in this case, is irrelevant. It's just there for its structural value. English grammar says we need a preposition there, so we have to just pick one.

In Esperanto, in those situations, we pick "je".

"Je" can be replaced by adverbializing the noun following it. The following are equivalent:

Mi spektis la programon je la televidilo.
Mi spektis la programon televidile.

Both just mean I watched the show, and the tv was involved.

During a time in the past I preferred only the adverbial method of expression, and tried not to use "je" at all because it seemed like a clumsy hack to me. I now think I was a bit hasty in thinking that, and now just consider it to be an alternate form I can use to add variety to what I'm saying.