guide

roll syntax is roll <dice> <modifier> <repeats>
<dice> is the number and size of the dice to roll, e.g. 2d6, 1d20
<modifier> is what to add at the end of the roll, e.g. +5, -5
<repeats> is how many times to repeat the roll, e.g. x2 for advantage, or x3 for rolling three attacks at once

examples

roll 1d20 +6 or roll 6 rolls a skill check with a +6 modifier
roll 2d6 +5 x3 or 2d6 5 x3 rolls greatsword damage with a +5 modifier three times
roll 1d20 1d4 -3 x2 or d20 d4 -3 x rolls a stealth check with a -3 modifier, guidance, and disadvantage

plus signs can be omitted
- e.g. roll 1d20 +6 x2 is the same as roll 1d20 6 x2
if <dice> doesn't specify a count, it defaults to 1
- e.g. roll 1d20 6 x2 is the same as roll d20 6 x2
if <dice> is omitted entirely, it defaults to 1d20
- e.g. roll d20 6 x2 is the same as roll 6 x2
roll can be omitted entirely if at least two parameters are provided
- e.g. roll 6 x2 is the same as 6 x2
if <repeats> doesn't specify a count, it defaults to 2
- e.g. 6 x2 is the same as 6 x