1.2 Components of verbs

1.2.1 6 components (2 + 4)
Every verb form has a stem and an ending.
Other components include augment, thematic vowel, tense sign and mood sign are added accordingly to the above 2 components. Usually, some phonetical change might take place when these components combine.
You should be able to get familiar with the principal parts.

1.2.2 Stem and principal parts
Every verb has 2 stems: verb stem and tense stem
Usually, Ω verbs have only one verb stem, but ΜΙverbs have two.
Such as:
τ?θημι: θη-/θει-, θε-
δ?δωμι δω-/δου-, δο-
Most forms use the short stem.

1.2.3 6 tense systems (principal parts)
According to the tense stem, verb can be categorized into 6 tense systems (6 principal parts).
a Present: present and imperfect
b Future: future active and future middle
c Aorist active: 1st and 2nd aorist active and middle
d Perfect active: 1st and 2nd perfect, pluperfect and future perfect
e Perfect middle: perfect, pluperfect and future perfect middle and passive,
f Aorist passive: 1st and 2nd aorist passive and future passive

1.2.4 Every tense system has a present indicative 1st person singular form called principal parts.

Summary of principal parts
Some verbs miss one or more principal parts. One reason is that they don’t appear in Greek texts while another reason is that the verb itself doesn’t allow such form.