Trucks: Lows or Highs?

Just wondering what the difference was between thunder (or any other truck company) lows and highs?

They are just the heights of the trucks. Little guide is

The truck height can vary. Low trucks make flip tricks easier and add some stability, but with lower trucks you will want smaller wheels. High trucks allow you to use larger wheels, which will help when skateboarding at higher speeds or long distances.

If you are a new skateboarder, I recommend using medium trucks, unless you know for sure that you want to use your skateboard for street or cruising. For street, low trucks are good and for cruising, medium or high trucks are a good choice.

i want to do cruising and tricks, what should i get? Thunders dont hav mids.

Its all preference, everyone has their own opinion. Personally I have no idea what mine are, I have spacers though because I like my boards uber loose.

Thunders should have a mid, they normally have yellow bushings on the raws. I find they are a bit lower than your usual mids though.
If you are after trucks for cuising around, go for a set of mids. Allows you skate bigger wheels and also have your trucks looser. This allows you to carve a lot more and have fun.
If you do get wheel bite you can put some riser pads underneath to give yourself some more clearance.