Can someone explain how careers work? I am overall confused since I'm coming from 5E D&D. Thank you!

Sorry for the very late response. Not sure exactly what you want to know, so here's an attempt to summarise everything about careers.

1. They're definitely not to be confused with D&D classes. You will change career multiple times (if your character lives long enough), and only have one career at a time.
2. Get a career at character creation - either choose one, or pick three at random and choose one, depending on what method of character creation is being used. This career is what your character was doing before they set off on a life of adventure, or may still be doing depending on the career.
3. Each career has a set of 10 advances to choose from: actions, talents, skill training or speciality, fortune dice, wounds, conservative stance, reckless stance. These are listed on your career sheet and are what you can spend your XP on in order to complete your current career. Each career advance costs 1 XP.
   • You can also spend XP on improving primary characteristics (the 2 characteristics listed on your career sheet). This costs a number of XP equal to what you're raising the characteristic to, e.g. raising Strength from 3 to 4 costs 4 XP. This counts as a career advance.
   • You can also spend XP on advances not listed on your career sheet. These are non-career advances, and they cost an additional XP each. This does not count towards completing your career.
4. There are also 4 "fixed advances" that you have to spend XP on to complete your career: action card, talent, skill training or speciality, wound.
   • Note that these do not count against the limits on your career advances. So if your career lists 2 action card advances (for example), you could actually purchase 3 action cards during that career, 1 fixed advance and 2 career advances.
   • This also means that you will only purchase 6 of the 10 career advances available to your career.
5. Once you have purchased 10 career advances (4 fixed advances plus 6 optional), you have completed that career. You may then purchase the dedication bonus for 1 XP, which means you keep the career special ability permanently, learn a free speciality for each skill that was trained as a career advance, and spend one fewer advances to enter a new career (to a minimum of 1).
6. Whether or not you purchase the dedication bonus, you can now move to a new career: choose any allowed by your race (note, some have other restrictions). This costs 4 XP minus 1 for each trait the current and new career have in common, to a minimum of 1. So if your current career has 4 traits in common with the new career, it costs 1 XP to enter the new career.
   • Note that Reiklanders can enter a new career for 0 XP due to their Adaptable racial ability.
   • Note that the Specialist trait never counts as being in common across 2 careers.
7. Finally, you can leave your career at any time and enter a new one (at the GM's discretion), even if you haven't completed the current one, but you can't get the dedication bonus and will lose your current career's special ability.

Some other notes:

1. When spending XP on career advances for actions or talents, these can be any from any category (although your GM may put their own restrictions on this).
2. When spending XP on career advances for skill training or specialities, these have to be for your career skills (the 4 or 5 skills listed on your career card).
   • Note that you can only have 1 level of training per level your character is at, so no purchasing 2 levels of training for a skill in your first career.
3. When spending XP on career advances for fortune dice, this means adding 1 fortune die to all rolls involving 1 of your primary characteristics.
4. You do not get the trappings of a career for free, but you aren't obliged to buy them either. They're just suggestions for what someone in that career would be equipped with. (I only mention this because it's different to other editions of WFRP.)

I think that's everything, but any other questions just let us know.