About filters, they are very versatile and flexible. For step scores, I can filter for scores above or below a certain cutoff, or whether a score exists at all. I can choose what type of school, country (for international schools), year of graduation, number of research experiences, etc. ERAS does come with some built in filters, but those are very basic -- all US grads, or everyone selected for an interview, etc. Each program needs to build a filter to find what it wants. So, for example, my filter for "Applicant ready to review" is Application + Transcript + >= 3 LOR's + PS + (USMLE Step 1 or COMLEX Level 1) + MSPE. My IMG filter adds Step 2 CK.
How do I review applications? There's no way I can read all applications -- I get >2000 for only 200 or so interviews. Every program will do things differently. I start by looking to see if the applicant has ever worked / studied at my institution -- if so, I at least review their application briefly. After that, I pull out all of the applications that have USMLE scores well below our target -- they get rejected without further review. We state a USMLE minimum on our website. I then look at all applications with prior GME training at least briefly (because their YOG may be a bit in the past), and then filter out anyone whose YOG is too far in the past (also on our website). That narrows the pool, and then we start reviewing applications. This is a single example -- I'm sure each program is different.