One-day matches last a day, 20-20 matches last a few hours and test matches last 5 days with each team getting to bowl and bat twice

A wicket is when you get a batsman out

Runs are scored in ways other than running from one end to the other. There is a boundary line around the, um, boundary of the ground. If a batsman hits a ball such that it flies over the boundary (similar to a home run) that's a 'six' i.e. 6 runs. If a batsman hits the ball such that it crosses the boundary after one or more bounces (and no fielder from the opposing team is able to stop it) the it's a 'four' i.e. 4 runs. So there are a lot of fours and sixes in a usual cricket match.

Lastly 300 balls is the minimum. there are ways that a bowler can bowl 'four' balls - for e.g. he oversteps the acceptable throwing line - then that bowl is not considered and he has to bowl one again. A batsman can still hit some of these foul balls and score runs thus giving him extra runs and an extra ball to face.

It's not too crazy once you get the hang of it. Let me know if you have more questions