u gotta go to the sequencer, and then u hit record (not play and record, just record) and then you put the lil cross hair on the box you want, then you press the pad and it puts the dot there . . . good shit . . .
On the older roland r-8 and a couple of other older drum machines it was the exact same way where you use the grid to put dots in the resolution tick boxes on a bar, it was step editing.
The mpc was probably created for trained musicians that can think of their music abstractly rather than in the easily understandable graphics that make it accessable to all.
Try using a DMX! Its a crash course in time signatures and makes the MPC seem luxurious!