herewego

Been a while since new hire for me so the exact procedure and timeline is quite fuzzy but generally<
Early in indoc or systems you will get a presentation that shows all the domiciles for your type aircraft and a lesson on how to fill out a "Dream sheet" of your desired base in order of preference.
Those dream sheets are processed by HQ in seniority order, with the most senior person in class having his domicile awarded, then number two, 3, etc down to the most jr new hire who gets the last slot available.
Your assignment will be awarded the last week of systems, before sim.
After that there is a Monthly Domicile Vacancy Report (DVR) posted online about the 20th of the month, with a mostly inaccurate guestimate of what slots will be be available for transfers, transitions and upgrades. The senior bases are most accurate but even they are almost as good as a monkey throwing a dart at a board, with slots at the more jr bases being totally worthless as they are getting backfilled as those pilots move to the more desirable bases.
These awards are done the last few days of the month with class dates about 5-9 weeks out, or transfers effective the first day of the next month ( Nov 1st transfers will be awarded about Sept 29th), so that fly your October schedule at your old domicile but can bid your new domicile schedule during the October PBS run .
Class seniority is covered earlier in this thread but is basically Date of Hire (previous employee as a ramper, dispatcher, Flight attendant, intern, cadet) then true new hires based on last four of your social security number with XXX-XX-0001 being senior to XXX-XX-9000.