Yes, you do have to memorize these, and it can seem like it is nothing like the other declensions but there are similarities. There are also very good reasons for the forms if you get interested in linguistics and decide to study that. Fortunately, there's a lot of duplication in the plural cases (dative=ablative, nominative=accusative) Anyways:
NOM SING - memorize PLUR - same as accusative plural, also very similar to English and Romance languages
GEN SING - every declension's genitive singular except 2nd decl. originally ended in S (remember paterfamilias, familia, familias) PLUR all declension' genitive plural ends in -um
DAT SING - same as those irregular adjectives you'll be learning soon
DAT/ABL PLUR -ibus looks like that -abus found in the first declension
ACC SING - all of them end in M, just the vowel before the M changes PLUR - ends in S like all of them
ABL SING - ends in a vowel, like all of them
flebile nescio quid queritur lyra, flebile lingua murmurat exanimis, respondent flebile ripae