Roll20 is easy but you can roll physical dice if you want. Honor system.
Recommend using Beyond 20 to send D&D Beyond dice rolls to Roll20.
Player absences
Sometimes players may miss a session. When that happens the following rules apply.
Their character fades to the background. They are around in-game but they won't speak up during role-playing unless directly asked and remain out of combat.
Their character will not receive XP during the session.
They may or may not receive any treasure, that's up to the party.
After many absences, the player might be asked to give up their seat or become an on-call player.