Past Tense

For now let's stick with the -masu form of verbs

PAST = MASU arrow image MASHITA

たべます tabemasu (to eat) arrow image たべました tabemashita (ate)
のみます nomimasu (to drink) arrow image のみました nomimashita (drank)

PAST NEGATIVE = MASU arrow image MASEN DESHITA

たべます tabemasu (to eat) arrow image たべません　でした tabemasen deshita (didn't eat)
のみます nomimasu (to drink) arrow image のみません　でした nomimasen deshita (didn't drink)

 The "-masen" is the negative part