I'm not a PTO, but I'll try straighten this out.
Firstly, Submit an application on these forums, there's a nice big button at the top.
Make sure you've answered all questions to the best of your ability, and with honesty!, then submit!
Then a waiting game begins, Applications are looked at in batches, not a single application at a time (again, this is speculation from being a cop).
If you're accepted, you'll receive a PM similar to this:
Hi, You have been accepted, please come onto TS for an interview with a PTO. Once the interview has been completed, and if passed, you will be trained and white listed. Please contact a PTO when ready. - CSI Mitch
At this point you need to join the appropriate room on teamspeak called "Want To Join The Police":
If no-one speaks to you in the next (roughly) 20 - 30 minutes, message a PTO in a channel below, It's usually better to contact one in a meeting room as shown above as they are most likely not on duty at that moment in time.
Be respectful,
This is good:
<11:21:07> "PC Neo": Hey, I've been accepted into the Police and told I need to talk to a PTO, Are you available to do my interview?
This is bad:
<11:21:09> "PC Neo": Hello
<11:21:13> "PC Neo": c'mon i've been waiting
<11:21:16> "PC Neo": helllooo????
If they don't get back to you, they're either busy, or not available, Move down the list to the next [PTO]
Change your message to something like
<11:21:07> "PC Neo": Hey, I've been accepted into the Police and told I need to talk to a PTO, I attempted to contact SPC Name [PTO], but they're not there, Are you available to do my interview?
Repeat, and proceed, Someone will eventually talk to you, I know this seems like a hassle but all police PTO's volunteer their time.
You'll then do your interview on teamspeak, they'll ask questions and scenarios to score up your application to be finally accepted and white-listed, They'll let you know that you've passed or failed, and if passed, this is when you'll be added to the PNC, the Police National Computer.
This is read by a specific server admin whom usually checks it every few days when he's on but can take upto a week.
The best way to know if you're white-listed is to attempt after each restart... White-listing does not require a restart, but it's just better to do so, to check regularly.
If it has been a few days, or a week, Contact a PTO that is DI or above, to confirm the information is correct, always have your ARMA GUID Handy for this. In this time try to watch how the police play, don't keep running up-to them and causing them to ask you to stand back.
When you are white-listed, it's time to contact a PTO again for your Module training, This'll be more covered in the police handbook and the PTO.