Too little info, too many options. have a look at www-bicycletutor.com, www.parktool.com or www.sheldonbrown.com for help.
no
Trail bike is too vague, you have to specify which bike and how big jumps you're talking about.
if u have a 4 cluch and u want to o fast like over jumps or something u should be in 4th gear and if u only have a 2 clch then i guess 2nd gear
1st gear will always be your lowest gear no matter what bike you are on.
First of all get the bike from mauvile cities bike shop second choose it in the bag and ride it now your on the bike the cool thing about this bike is you can do: wheelies, jumps and bunny hops.
The draisine aka boneshaker aka hobbyhorse was a true gearless bike
One can create bike jumps in many different ways. An individual can buy plastic already made bike jumps if they would like. They can also make them out of dirt and gravel. A popular way of making bike jumps would be out of ply wood bought at the local hardware store.
practice
if your talking about starting the engine up, its best to crank a bike up in neutral but you can in first if you hold the clutch in if you mean riding the bike if you try to go in say fourth gear the bike is likely to stall
Cable too slack.
Dirt bike jumps is a type of sport categorized a motor sports. there are several different types of jumps involved in dirk bike jumping. Usually people learn the different jumps and moves from on hands experience at a local dirt track built for motorcycles only.
I have no idea what you mean by "gear bike", so the question can't be answered.