See

miru: see, look, watch

minai : see + not
mimasu : see (polite)
miru : see
mirutoki : see+when
mireba : see + if
miro : see(imperative)

Basic 6 patterns of verb conjugation.
-nai
-masu
-(base)
-toki
-eba
-o/e etc

okuru : send

okura-nai : send + not
okuri-masu : send (polite)
okuru : send
okuru-toki : send + when
okur-eba : send + if
okure : send (imperative)

kau : buy

kawa-nai : buy + not
kai-masu : buy(polite)
kau : buy
kau-toki : buy+when
ka-eba : buy + if
kae : buy (imperative)

uru : sell

ura-nai : sell + not
uri-masu : sell (polite)
uru : sell
uru-toki : sell + when
ur-eba : sell + if
ure : sell (imperative)

-nai, -masu, original , -toki , eba , o,e should be learnt by speaking repeatedly like an incantation.
When those words (-nai, -masu,...) are attached to verbs, verbs should be conjugated.
But it is not a big problem to make an mistake in conjugating verbs in our conversation.

terebi : TV
Watashi wa terebi o minai. : I, TV, watch not : I don't watch TV.

If you say "Watashi wa terebi o miru nai.", Japanese people understand you don't watch TV.