One common reason for the gears sticking is incorect oil type, motorcycles have wet clutch and specific motorcycle oil must be used, otherwise the clutch drags and gears are hard to shift.Aside from any major problems with the transmission itself, is your clutch working properly? Is it set correctly and fully disengaged when it is not being used. I would start here. You may need new plates in your clutch itself.
6 gears and neutral.
It depends on the bike if the engine of bike is heavy it has more gears. Usually 5 gears are max gears.
6
It has 5 gears mine has 6 gears
Depending on the bike yes most adult sized bikes have gears
The left leg shift.
they all have stuff sticking out of them
No a motorcycle is way harder different gears and stuff so a car is easier
you have to take apart the motor completely
Yes motorcycle gears will shift up and down.
The only time you need to use a clutch on a motorcycle is when shifting into First, You aren't going to do any more damage to the gears than if you used the clutch. Its designed to work that way.
the kawasaki 125 has 5 speed