Decide if you're going to use a free app such as "ID Photo Studio" or have your passport size picture taken at Walgreens, CVS, etc. If you're going to use the app go ahead and take your picture so it's ready for the online application.
Complete the online application. Upload your passport photo. Make your payment for either a 5 year ($100) or 10 year ($200) license. At the end you'll print off a summary page.
Contact your county sheriff's office to see if an appointment is necessary to get your fingerprints taken. Ask what the cost is and what form of payment they accept.
Take the summary page, the original certificate* you received from the OSDA class (not a copy), your passport photos (if you didn't upload them) to your county sheriff's office. The sheriff's office will take your fingerprints and send all of your documents to the OSBI.
Wait for your license to come in the mail.
* There is a $5 fee to re-print a class certificate