https://www.youtube.com/watch?v=X0LyvD9lkL8

Every verb concept comes with a pair of words.
One of them is Imperfective, the other Perfective

Пить is the imperfective verb for "to drink"
Выпить is the perfective verb for "to drink"

Perfective is used for completed, one time actions.
Imperfective is used for ongoing, repeated actions.

Пил = "was drinking", "drank (a bit)", "drank (every day)"
Выпил = "finished drinking", "drank (the whole thing)"

About 99.97% of Russian verbs have an Imperfective-Perfective pair

Most often, one verb will be imperfective, and the perfective will be the same root with an added prefix. по- being the most common
Here with пить you can see that the prefix вы- is what constitutes the perfective.

Sometimes an extra in-syllable is added to form imperfective from perfective -ыв-

https://en.wiktionary.org/wiki/%D0%B...B0%D1%82%D1%8C


A common hierarchy structure is:

ROOT [imperfective] -pair- prefix1-ROOT [perfective]

prefix2-ROO-infix-T -pair- prefix2-ROOT [perfective]

prefix3-ROO-infix-T -pair- prefix3-ROOT [perfective]

prefix4-ROO-infix-T -pair- prefix4-ROOT [perfective]

The first pair would constitute the most basic meaning. "To hit" for instance. The other pairs would make up more flavoured types, with a new prefix. "To knock off", or "To break up"
So the most basic imperfective root is then used with prefixes for all the perfective forms, while all the *other* imperfectives use a new slightly altered version of the base root.

https://en.wiktionary.org/wiki/%D0%B1%D0%B8%D1%82%D1%8C

Also, you will notice a vague correlation between Imperfective verbs ending in -ать, and Perfective verbs ending in -ить. This is certainly no rule, it is often not the case, but more often *is* the case.