Hello,
I have read this nice tutorial about movement and I tried to do the same thing, but on the graph screen. I tried to add movement in the second dimension. For some reason it doesn't work - once any of the arrow keys is pressed, the pixel goes to the top of the screen and can only be moved horizontally.
AxesOff:
FnOff:
ClrDraw:
ClrHome:
32->Y:
48->X:
Repeat K=45:
Pxl-On(Y,X:
Repeat Ans:
Getkey->K:
End:
ClrDraw:
X+(K=26 and X<94)-(K=24 and X>0)->X:
Y+(K=34 and Y<62)-(K=25 and Y>0)->Y:
End:

Also I know that this is a very simple subject, but I'm just a beginner and I can't figure this by myself.

Exactly what dinosteven said. Generally in TI-BASIC you should avoid using X and Y because they get updated by drawing commands.

By the way, what's better for stopping the pixel from going out of bounds?
DincoC's method or using a max and min command? I've always used max and min, cause that's what's on the TIBD.

What symbols?
EDIT:
Oh the symbols for the variables. Hmmm.... It works on my calc. Make sure every variable is updated, you probably updated the pxl-on() but not the part where it moves up/down.

Yeah, I updated all of them. Besides the lack of vertical movement, there is also another bug. When I move the pixel to the left, it goes ok for 13 steps. On the 14th step it jumps one step left and one step down, then it goes to the left for another 8 steps and on the 9th jumps one left and one up. When going back right it does a similar thing, except it jumps up.

It works. Here's a screenie of me scrolling through the code and running it: