ok so on EXJUMP the program flips a sprite by writing 8 on SPCHR. why it doesn't work for me?

Because it doesn't write 8 on SPCHR. What it does is to ADD 8 to the definition number so the sprite will change to a flipped version of itself.

Ok..so ehmm...do i have to define my sprite looking to the left so it can work?

If you're using custom sprites, then yes. But is better to use the alternate version of SPCHR, which allows you to mirror the sprite without redefining the dimensions. SPCHR ID,U,V,W,H,Attribute On attribute, put #SPREVH+#SPSHOW to mirror the sprite.

ok yeah i know how to that. can you tell me how can i define sprites?

by using SPSET. The second version of SPSET is the one you're going to use the most, since is more customizable. If you mean creating a sprite and using it, first draw the sprites and save it as a file. Then load the sprite file on the main program.