Toilets use a wax ring for sealing the toilet to the drain pipe. 

 Usually a simple repair, shut off the water, flush and drain/wipe water from the bowl, and undo the two/four bolts/nuts holding the toilet to the floor. 

 Remove the toilet and replace the wax ring.

Check for it leaking anywhere else, tank joint, pipe connection, or cracks in bowl or tank(this is toilet replacement problem).