So why it isn't "A garázs a háznál van."?
That would be "The garage is by the house." Mellett makes the two buildings neatly aligned, -nál makes it sound here that the garage is just somewhere in the house's vicinity.
Aren't "beside" and "next to" the same?
Pretty much, yes.
Why isn't it " The house is next to the garage"? I thought words like mellett are combined by the word before. So "the house is by.." - ... a ház mellett van
mellett goes with the thing before in the way that preposition go with the thing after in English.
So a ház mellett is "by the house", and ... a ház mellett van is "... is by the house".
mellett is right after a ház, just as "by" is right in front of "the house".
This has been something taught over and over:
X mellett Y áll = Y is next to X
Y X mellett áll = Y is next to X
Y áll X mellett = Y is next to X
I do advice you going back to older courses on these topics, and analyze the usage there.
A garage a ház mellett van.... You typed in English not Hungarian! Haha. No i didnt