I understand what everyone is saying about multiple meanings for "hacer" but the translation says "You MAKE your own shirts" but since hacer may also mean "have" ("hacer una fiesta" = "to have a party"), how do I know that this sentence is not saying "I HAVE my own shirts? - Or is it never used to mean that, and I simply need to memorize it?
Hacer is to do/to make. To have is a different word entirely, which is tener. Tener typically refers to physically having something (e.g. I have this pen), with the exception of age because we "have years" in Spanish. Hacer una fiesta is not a literal translation; it's more like a phrase for have a party, as we know it in English.
In case if it helps.... Hacer can mean any of these- accomplish, form, put, take, constitute, construct, keep, cause, pose, give, render, lay, perform, raise, inure, fabricate, carry out, hold, behave, be, fashion, work out, do, transact, run, make up, use, have, generate, get, act, create, imagine, make, effect, work, build, observe, prosecute
The rule of thumb is to say that generally adjectives go after nouns, but that is not the case here. Some adjectives go before nouns simply because they are not as descriptive as they are defining. For instance, one would say "El gran hombre" rather than "El hombre gran" because it's more of who he is rather than what traits he has.
A good example in English would be the difference between a wise man and a man that is wise. Dumbledore (yes, from Harry Potter) was a wise man, but your grandfather may just be a man who is wise. Or the difference between hot chocolate and chocolate that's hot. (That's actually a dilemma in English when it comes to comma usage separating coordinating and noncoordinating adjectives)
Sadly, this is one of those things where you have to memorize what adjectives commonly go before nouns.