you need to select "mic" in the input settings:
hold down the "view" button to enter the system settings and go to page 3/10
select "mic" for the input
to have both your guitar and the mic working together, set input 1 to "guitar" and input 2 to "mic" and prepare double patches: guitar in path A and mic in path B
One other thing - you need to use a dynamic (not condenser) mic. If you have a condenser mic you will need to provide the phantom power it requires using another device; the X3L does not provide phantom power.