There are four major verbs in Russian which have entirely irregular conjugations:
| хотетьimpf to want | |
|---|---|
| хочу | хотим |
| хочешь | хотите |
| хочет | хотят |
| бежатьimpf to run | |
|---|---|
| бегу | бежим |
| бежишь | бежите |
| бежит | бегут |
| датьpf to give | |
|---|---|
| дам | дадим |
| дашь | дадите |
| даст | дадут |
| естьimpf to eat | |
|---|---|
| ем | едим |
| ещь | едите |
| ест | едят |
Prefixed versions of these verbs and many verbs derived from them are comjugated in the same irregular ways. Ex: выесть, обдать
The above verbs are also important because they're so common. As for other irregular verbs, it's difficult to quantify them all. If you are unsure about a verb's conjugation, look it up in a dictionary (or an online dictionary like Wiktionary- an awesome source!). Don't let the exceptions to the rules intimidate you- you will naturally recall more and more of these irregular conjugations as you learn Russian :)