So other than logging in, hating the look of the thing and thinking what am I doing, I just find a random race and thats it? Do you need to qualify for them in any way?
Racing is only a small part of it, most people 'just ride', then progress to the training sessions and plans on there.
Majority of races, info & results are listed by:
https://www.zwiftpower.com/race.php | Much of the results here are 'auto' linked to rider data from Stava rides. Sometimes these links don't work. Some race admins are good, some are not/non-existent.
No qualification for races, just enter from the 'start screen' when starting Zwift. You can then ride the course as normal but you will get a timer on the bottom left (until race start). A few minutes before the start you'll get transferred to a 'holding pen' with everyone else in the race. you're able to warm up here without actually 'moving' on screen (on turbo's!). You can join this pen early and there's a 'chat box' showing other riders joining along with a an area to 'chat'. When you 'chat' in game you will only see chatter from those in the same race. Your 'rider panel' will only show riders in the same race (but everyone riding on the course will still be displayed).
Most race organisers request for you to add some race initials after your name, some even the CAT level you're riding. Although most rides require you to 'enter' the correct CAT, it is done in different ways (depending on the ride). Some from that start screen (you'll see different races for each), others are a 'mass start' and you are asked to edit your name, or just categorised by your resulting w/kg average after the finish (like OMS getting 'upgraded' to CAT A, even when having 'B' in his screen name iirc). Some races 'upgrade' you to a higher CAT, some exclude you from results as you 'exceed' the CAT limits for the race you entered (I got caught out by this a number of times when starting out).
Side note: many riders 'cheat' by having a low rider weight entered, occasionally you'll see riders get declassified as their w/kg will end up exceptionally high and they will need to submit real world data to back this up (I believe 'outside' Strava rides qualify). Everyone in CAT A has to have a HRM to qualify. Also riders with ZP (zwiftpower) calculated from a 'dumb' (non-smart) turbo trainer are not allowed to win races.
Hope most of that makes sense. I should maybe put a thread together on how to get into Zwift racing!?