[sakaeyellow]

Just want to add that Japanese also has past progressive, e.g.

飲んでいました/飲んでいた＝was drinking

And ている does not necessarily correspond to English "ing". If a verb is instantaneous, i.e. the action takes place and finishes immediately, then ている functions like English perfect tense. Examples are:

死んでいる＝is dead (not dying)
結婚している＝is married (not in the process of getting married)

ている indicates that the results of those instantaneous verbs continue.