Think of a taper-crimp die like a funnel - a cone. It starts wide, and then tapers narrower. As the shell is pushed up into the die, it goes into the taper, and the case gets squished into the side of the bullet.
This is a sketch of the inside of a rifle seating die, but a pistol die works the same, for a roll crimp.
See the two places circled in red? Notice they are curved inward? As the case is shoved up into the die, the case-mouth hits that (it's called the "crimping shoulder") and the curve forces the case-mouth to "roll" into the bullet. That would be a "roll crimp".
No, you can't do both from the same die. The two dies are built differently.
Normally a revolver cartridge and a rifle cartridge die will be made with a roll crimp, while an automatic pistol cartridge die will be made with a taper crimp.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.