If you are going to continue on to Functional Greek, you will have to memorize these words, so you might as well do it now. If you are only learning Church Greek, then memorization is recommended but optional.
Conjunctions occur 18,180 times in the New Testament. If you would memorize four conjunctions, καί, δέ, γάρ, and ὅτι, you would know 13,474 of these occurrences, but we will learn a few more.
ἀλλά (ἀλλ᾿), but, yet, except (638)
γάρ, for, then (1,041)
δέ (δ᾽ ), but, and (2,792)
ἐάν, if, when (334)
εἰ, if (502)
ἤ, or, than (343)
ἵνα, in order that, that (663)
καί, and, even, also, namely (9,018)
ὅτε, when (103)
ὅτι, that, since, because (1,296)
οὕτως, thus, so, in this manner (208)
οὖν, therefore, then, accordingly (499)
τε, and (so), so (215)
ὡς, as, like, when, that, how, about (504)