Vav-conversive
A prefixed ו can flip the usual force of a perfect or imperfect. Narrative past in the Torah is mostly this form.
Wayyiqtol
Imperfect (yiqtol) with וַ, typically a patah and dagesh in the prefix consonant, is the backbone of biblical narrative: "and he said," "and it was." Grammars also call it vav-consecutive or the consecutive imperfect.
and he said
Gen 1:3and there was; and it came to pass
Gen 1:3and he saw
Gen 1:4Weqatal
Perfect with וְ often continues future or modal force after an imperfect, especially in law and instruction. It is not a simple past. Context, not the letters ו alone, decides.
and you shall love
Deut 6:5Not modern "and"
Israeli Hebrew still starts sentences with ו, but it does not convert tense this way. Reading Genesis as if every וַי־ were only "and" plus a future will scramble the story.
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The perfect and the imperfect
Biblical verbs mark aspect more than calendar tense. Perfect (qatal) and imperfect (yiqtol) need context, and often a vav.
Genesis 1 word by word
The opening of the Torah is the usual first connected text: a few roots, heavy use of wayyiqtol, and the object marker.
The binyanim
Hebrew verbs inflect in stems (binyanim) that shift voice and intensity on the same root.