How do you calculate voltage in this simple circuit..don't understand electricity help!!!?

This uses several techniques - addition of resistors in series and parallel and the potential divider formula.  If you don't understand, take a look at the videos in the link.  There's a whole set of other videos in the same channel covering basics of circuits.

The 3? and 5? are in series (total=8?).  Imagine replacing the 5? and 3? with an 8?.

The circuit is then two 8?s in parallel, and a 2? in series.

Two 8?s in parallel = 4?.

The circuit is then a 2? in series with a 4?.

Voltage across the 4? is 12 x (4/(2+4)) = 12 x 2/3 = 8V  (potential divider formula - see 2nd link)

This means the 3?+5? has 8V across it.  Using the potential divider formula (or common sense) give the voltage across the 5? is 8 x (5/5+3) = 5V