level 3 trick

A level 3 trick is "Ride over 10 x 10 cm obstacle."

I'm not clear on this. Could someone describe this obstacle a bit better so I
could visualize it?

Yeah, a 10 x 10 cm object is merely a 2 dimensional hypothetical portion of a
plane. I think the third dimension is up to you. Like riding over a piec of
lumber 10 cm tall and 10 cm thick and (let's say) one foot long (or
whatever). Brian

Mike,

There are 2.54 cm to the inch making 10 cm approximately 3.94". Call it
4" to make the numbers easy. Obtain a standard 2x4 stud and cut yourself
three lengths anywhere from 16" to 24" depending on how well you can
aim. Practice riding over just one 2x4 first. When you can do that okay,
screw studs 2 and 3 together which will give you 3" by about 3-3/8".
Place a single stud before the joined pair to make a mini built-up.
Practice riding over that. When you can ride over in all crank positions
you've got it (almost). Take away the entry stud and ride over just the
joined pairs in all crank positions in both directions. When you can do
that, turn the block a 1/4 turn and ride over that to the tune of
3-3/8". For the final 4" nail your block to the end of a piece of 3/4"
plywood 16" by 24" for a final height of 4-1/8". If you can ride over
that in all crank positions you'll have no problems on a 4"x4" block.
Flip over the block and plywood for a ramp and practice riding off it.
Practice hard and good luck.

"The Muniac"