Context. For example, "soweli loje" or red animal could mean anything, but given that there's a fox right there, or that we're commenting on a post that has a picture of a fox, I'm probably talking about that and not something completely random and out of context.

If this makes you think, "oh man that seems really limited" yes. That is intentional. Its like I said, its auxiliary. For some, trying to think in simple terms on purpose, is a good enough reason to learn it, but for me, the ability to speak to people who's native language is a variety of languages which learning even one of them could be a endeavor, it can be worthwhile. Afterall, without it, I can only "point and speak", use 1 or two words from the language, or communicate through pictures (although using a translator is also an option, but I have yet to see an online community where translating back and forth is an expectation, I have however seen toki pona communities where people's primary language is all kinds of other languages) so in that way, you can actually communicate more complex things than you'd be able to without it.