yes.
사랑해(saranghae) is more informal. You can use this word to really friendly girl or boy friend.
사랑해요(saranghaeyo) can be used for older people like parents. '요(yo)' makes it polite.
사랑합니다(saranghamnida) is formal experession generally.
That's right as you know.

i've heard just saranghae or saranghaeyo. so is this more informal...maybe? than that sarang hamnida??

it means "people"yep?

Oh, I see. Thanks a lot . It was really helpful.

"sarang hamnida" is a polite way of saying "I love you".

"sarang handago" means "that I love" and it's kind of quotation.

사랑한다고 말해 줘.
sarang handago malhae jwo.
-> Tell me that you love me.

A: 뭐라고? (mworago?) : What did you say?
B: 사랑한다고! (sarang handago) : (I said that) I love you!


Hope this helps!
:-)