How to add username to table if is in group?

How to make it so if a player joins the game. And player:isingroup(GroupId) it adds his username to the a specific table?

You basically said it.

local NameTable = {}
game.Players.PlayerAdded:Connect(function()
	if player:IsInGroup(groupId) then
		table.insert(NameTable,player.Name)
	end
end)