You fill out an application online. In a week or two you will get a call or an email invite (I got both) to come down to the office for an interview and also to get placed if you are accepted. You will be drug tested same day so make sure you won't have a problem passing a urine drug test.
Prepare to basically spend your whole day there. The main questions they will ask you are what your availability is, what area you live in (they try as much as possible to place you at a post that is very close to your home to minimize the commute), and why you are interested in security. Be honest about it, but don't sound desperate. I needed to leave my old job because my hours were cut so severely and I needed a job with a more steady schedule, and security can offer you that for the most part. Predictable hours, predictable pay (sometimes you will need to work overtime with only a couple minutes notice; think right before your shift is scheduled to end, but so far, I haven't had to), and the posts are pretty simple to handle with the exception of standing most of your shift. They will ask if you can handle standing for long periods of time; be honest about this too. They don't want to place people they don't think can do the job.
After the interview you will be asked to go back to the lobby. You will need to log on to your portal thing and sign off on the drug test, so that you can urinate into a cup. You will know in a few minutes if you have passed the test or not. Once you have passed it, you will then be called in by the scheduling manager so that they can find a post and schedule that works for you. Background check will also be performed. They are constantly hiring since they are always acquiring new posts. They mainly contract with retail grocery stores (some of their posts are ports), and are always acquiring new stores that want to hire security, so there is always something for everyone most times, unless your availability is super limited. I did see someone unable to get a schedule because they had very limited availability. Although availability is important, it is also important to be honest about it. I let them know that although I can work any shift, I would prefer day or swing shifts and would prefer to work Monday through Friday. They were able to find me a post that met this request, and more than exceeded my expectations.
In case you're wondering, I accepted the job offer, since I liked the schedule. Since the day was ending soon, I was asked to come back the next day to be fitted for my uniform and to get set up for my schedule and fill out orientation paperwork. After I filled all that out, I was invited back the following week for actual orientation. People on glassdoor allege that the orientation is unpaid, but either that isn't true, or enough people complained, because it is definitely paid. You are expected to dress professionally for the orientation since that will be considered your official first day of work.. After orientation, I picked up my printed schedule, my ID badge, and my uniforms and started at my actual post the next day.
Also, people claimed that direct deposit was not available. I was able to sign up for direct deposit on the day of orientation, without issue. It has been accepted and approved already. They also offer the Brinks Visa Pay Card if you don't have a bank account but don't want to receive paper checks.
Anyway, I was given a good schedule at my post. I only work Monday through Thursday, with 3-day weekends every single weekends (which means I will almost never need to request time off unless I need a full week off or something), and yes, it is full-time. After 90 days of employment, you also have the option of switching to a different post. Pay and schedule may change, however so if you choose to do so, choose wisely.
Other than that, nothing else to report. Not hard to get the job; it's rare if they can't hire you. Obviously don't have any felonies, be able to pass a same-day drug test, and have open availability. They can usually tell who's going to make a good guard, and who isn't and they WILL fire you if you are found to be incompetent. Customer service at this job also goes a long way since you will be dealing with the public who will periodically come up to you asking questions. Be friendly, and smile.