Ugh I have such trouble with these...what's the best way to learn all of it?
Declension means that the word endings change according to the cases that are used. English doesn't have declension unless you count the genitive 's like "my mother's friend". Declensions refer to substantives, possessive pronouns etc while conjugations refers to verbs. In English you only have the "s" of the third person singular while in German the verb endings change according to the subject the verb refers to. Try to get familiar with grammatical terms, it's very helpful to understand the concept of a foreign language. As a native English speaker you have the disadvantage that many grammatical structures which are common in other languages simply don't exist in English. On the other hand, German speakers often struggle with the English tenses because the rules which tell you when to use a certain tense has to be used are much stricter than in German where we often use the Present Perfect in sentence where the Past Tense is obligatory in English.
What exactly is a declension? (sorry, I don't remember that term from learning German in school)
Yeah I overwhelm myself in general, sometimes I think I'm a slow learner...I wish I had more German friends in person to practice with but even then, in America, we'd probably speak English lol
Have you tried to invent English sentences where the words start with the declension endings? It's something I'm doing in order to learn Czech declensions. Czech has got 7 cases, so my sentences consist of 7 words while yours should be short sentences of 4 words. The sentences doesn't have to make sense. For example I invented the sentence "Alle Yaks essen unterm Ofen einen Outdoorfreak" to remember the declension endings of feminine substantives ending with "a" in the nominative case, for example "žena". So according to my sentences the endings are a - y - e - u - o - e - ou. Otherwise, I just practise a lot. It takes time and I think you shouldn't try to learn too much at once. It's really a matter of practise but I know how frustrating it is when you try to form a sentence and it takes you ages to figure out the correct case endings - or you think you used the correct ones and then a native speaker corrects the sentence and you realize that half of it is wrong :-).