You can make macros that roll dice for you. you can do it with a slash command if you're all old skool.
But there are menu items that will bring up dialogs if you prefer that approach.
Dice Macros show up to the left of the chat area as buttons.
Clicking the button rolls the appropriate dice and puts the result into chat for all to see.
How to:
Make a new dice macro: Select "Add Dice Macro" from the "Dice Macros" menu.
Give it a name (Example "Damage") then give a standard D&D dice notation damage text for it.
Like "3d6 + 12" or "d4 + 5d6 + 3". When you make a new macro, it will appear as a button next to the chat area.
Remove a dice macro: Select "Remove Dice Macro" from the "Dice Macros" menu.
Select the macro to be removed from the combo box in the dialog that comes up and hit ok. That macro will be removed.