Guild Wars 2

I have three right now, guard warrior thief, and I know most of their weaknesses and strengths but for now I don’t feel like leveling another class. How did you learn the weaknesses and strengths of other classes without leveling them up? for example did you find any guides describing how the profession works and learn from that (describing what their meta builds do and stuff like that)?

There’s some guides online. But is better to ask to your guild members to teach you something about they’re main class.
PvE isn’t the best situation to learn on other classes while in your’s, but you can try to play Structured PvP and see how other classes play.
In spvp you can see what’s the best offensive trait and build for a class or how a class can survive in a bad situation, how to take a position during a fight, how to make combos with your wepons and what kind of weapons/traits/runes work better together for a specific role.

For example: in spvp you learn how a guardian can dps hard and how a dps guardian can survive with a good timig with blind and block skills. Or see that necromancer have not a single defensive skill but can be a very good backline dps with Fear, DS and wells. Or how a mesmer can survive and flee from 2-3 enemies that focus him.

Ask to your friends or guild members and try some PvP situations (spectate mode can really help in that). That will grant you a good idea of how a class work and how you can fight against it.

It’s more time-consuming but the best way to really understand what other classes’ strengths and weaknesses are is to play them yourself. You don’t even have to level them up; you can go to the PvP lobby right after the new character tutorial and try out their skills and builds. However, if you go straight into matchmaking and don’t know what you’re doing your team might not be very happy about that. Custom arenas are generally a good place to start, or even fighting the training NPCs can give you a feel for how it works.

Are you asking how to beat pay them in PvE? Open world? Fractals/Dungeons? WvW or PvP?

Most classes play optimally very differently depending on the instance.

I’m assuming you’re either talking about pvp or wvw.

For wvw, you can google class guides, you can also try sites like metabattle and look at the meta builds for the classes in question. Sometimes they have info on their about expected weaknesses, counter classes to avoid etc and why.

For spvp, all the above applies; however, simply playing the class might be your best bet. The nice thing about spvp is that you don’t actually need to level to play the class, roll one….jump right in.

Personally, it was playing the class that made the most impact. Guides can be very informative, but I’m more of a hands-on learner. Thus, as I was reading a guide I would immediately go and practice what I just read.