Archbishop 10-K said:
I need help mainly with grammar stuff. For example, I have no clue what perfect active participles, gerundives, subjunctives, ablative of means, passive periphrastics, and all those things are. Also, I really have no clue how sentence structure works, so whenever I translate sentences, they come out all funky.
In other words, I probably need help starting with square 1.
Latin has sentence structure?
Most Latin sentences, at least in textbooks, are usually subject-object-verb, with a prepositional phrase ("In illo tempore: Dixit Jesus discipulis suis...") coming at the beginning of the sentence. Since the case endings are what's important, word order in Latin can vary and placing words out of order gives them extra emphasis. I've noticed, though, that many prayers like to place the object first, like in the Salve Regina: ("Et Jesum, benedictum fructum ventris tui, nobis post hoc exsilium ostende.")
If you're translating English into Latin, subject-object-verb is usually the best to stick with, and adjectives and genitives go after their noun.
The ablative of means is almost the same as the ablative of instrument. It's used to indicate the means by which the action is accomplished:
Dominum psalmis laudamus. We praise the Lord with (by means of) psalms.
The ablative can be a bit tricky sometimes, but once you realise it's actually three cases (Latin originally had 8; over time, three of them got condensed into one), it becomes a lot easier to figure out.
The original ablative, as the name suggests, was a case of removal, which is why it's used with
ex or to show motion away from, and can usually be translated
from.
The locative case was used to show "position where" or "time when", and is translated
in,
on, or
at.
The instrumental case denoted instrument or agent (the thing by which the verb is done), and is translated
by or
with.
The locative and instrumental cases have been dropped in Classical and Church Latin (although the locative survives in a few uses), and the ablative now has all these functions.
Hope this helps. I could type up a lot more on those other topics, but that's going to make for a really long and confusing post.

Pick a topic, and I'll try to help, then we can move on to the next. PM me if you'd prefer.