Setting up groups
Make sure every user right clicks on their name and hits the Register button when they login. This provides the server with their digital thumbprint and opens up additional options.
First thing you want to do is set up your groups. Right click on your server name at the top, select Edit, then the Groups tab. Under the dropdown, just type the name of a group you'd like to use for your leaders. Use something easy, like for example "Admin". Click add.
Under members on the left, go ahead and type in the names of the players you would like to add to your list and add them accordingly. If their name is italicized, it means they have not registered with the server and their permissions will not be saved.
Setting up permissions
Go ahead and hit the ACL tab now.
How mumble permissions work is that they go in a priority order going from the top down. Anything below will supercede the permissions above it. So the first ACL you see there has certain permissions which you cannot change. This is correct.
To modify permissions for the whole server, right click under the server name at the top, then click Edit. To edit permissions for specific channels, right click under the channel name and then click Edit.
What you then need to do is create a new ACL. At the very bottom where it says Users/Groups, expand the drop down and choose who you want to the permissions applied to. Look under the Context section. Do you want these permissions for that group of players to only be applied to all channels or just channels below it? Probably all channels. In your case, you want it for everyone so go ahead and select @all. This creates a new line under active ACLs and you can now choose to deny or allow whatever privileges you like.