Where the d10 shows up
- Weapons. Heavy crossbow, glaive, halberd and pike deal 1d10, and so do the longsword, battleaxe and warhammer used two-handed.
- Cantrips. Fire Bolt and Eldritch Blast both deal 1d10, which is why they get cast every single turn.
- Hit dice. Fighters, paladins and rangers roll a d10 per level, or take the fixed 6.
- Percentile rolls. Two d10s make a d100: one for the tens, one for the units.
Why the 0 means 10
A d10 is numbered 0 to 9 so that a pair of them can read 00 to 99 for percentile rolls. On its own, the 0 counts as 10. The roller above does that for you and draws the die exactly as it is marked.