Apply for the license. You will be issued a license which is good for 5 years during which time you must take either 1 credit or substitute at least 30 days.
NOTE: Don't confuse the Substitute License with the Substitute Authorization! The License is only issued to certified teachers and has no restrictions except that you cannot substitute more than one full semester in a classroom without the school seeking an exception from the state. The Authorization is only issued to non-certified teachers, has multiple restrictions and must be renewed annually! See the FAQ on the Substitute Authorization.