Online application, if you meet criteria of what they are looking for you will receive a follow up email to invite you to take a "battery of test" The test are fairly easy and I would suggest brushing up on your algebra slightly exp. 2x=10 (solve for x) Also look into mechanical aptitude test books or just look online. The last part of the test is a personality test in my opinion similar to taking a Myers Briggs.
Next phase you will receive a confirmation email stating that you passed and that your score is on file for a year. From there you will either be notified you have been selected for an interview or you may not receive an email for interview.
I applied August 28th 2015 for the Sweeny, Texas location and was selected 3 months later for an interview scheduled December 2015- this was a roller coaster for me because I am new to the industry and did not know the process could take so long. To be fair there was a huge set back with a new unit during this phase , I'm thinking this had to do with the delays.