- Drop lowest: "Roll five 6-sided dice, dropping the lowest two" →
5d6dl2
, If it helps, you can also use spaces:5d6 dl 2
- Keep highest: "Roll five 6-sided dice, keeping the highest three" →
5d6kh3
, If it helps, you can also use spaces:5d6 kh 3
- Arithmetic: You're a level 3 fighter, wielding a longsword (1d8), have a +3 Strength modifier, and a +2 magic weapon enchantment. Your attack roll is:
1d8 + 3 + 2
- Weapon Damage with Bonus Effects – Flaming Longsword(1d8 for weapon damage, 1d6 for fire damage, 3 for Strength bonus):
1d8 + 1d6 + 3
- Attack with advantage, roll 2d20 and keep the highest:
2d20kh
, as above you can use spacing if it helps:2d20 kh

If you have questions specific to certain systems rules, make a thread in the Tabletop subforum and we'll be happy to help.