questions...?????

맘 stands for 마음. If you see something that you really like and you want to have, you would feel like it comes into your mind. That's how 마음에 들다 means.

별로 is originally used with 안 + verb, like 별로 안 좋아. As it has been always used with negative verbs, 별로 gained the negative meaning after all. If 별로 is used as a noun, it means "not good". If it's used as an answer, it means the speaker wouldn't like to do something or don't like it or someone that much.

갖고 싶어 came from 가지고 싶어, and -고 싶다 = would like to do, want to do. -기 makes a verb stem into a noun, so 갖기 is a noun which means having.

주다 is also a auxiliary verb, it adds "for someone" to the meaning of the verb. 알려서 고마워(We never say this way) 알려줘서 고마워 = You informed me intentionally(you did it for me), thank you.

Happy birthday = 생일 축하해요