@GendarmeGo to the dice tab and click the button above circled in blue. Fill in the needed information and create your campaign.
Once your campaign is made, type in a roll and if wanted a description of it. Hit roll and you're done.
If you need to link the roll in a thread, click copy link. If you want to see a breakdown/the math behind the roll, click the roll ID. The roll system is very basic, however, and is mostly geared towards systems that use basic dice mechanics like DnD and not others like Exalted that use mechanics like degrees of success, double 10s, etc.
As of now, only one person can roll per campaign until Mahz gets around to further developing the roll system. Depending on who you're playing with, some people, like myself, might have a dedicated dice log/campaign for everything while others make a fresh campaign for each and every character they make. It all comes down to preference in the end.