in the trades/misc, there is an option to send gifts, under item market and above manage logs. so, the question is, that, sending other people gift, and receiving gifts from other people, how does it work? is it good? what is the use of having such feature?

It's just a way to say thank you or good job. It shows on their profile otherwise it really does nothing.

Adding on to catcherpro, it's a way of sending items to a person after a contest, etc... It's not much different than making a trade, really. The only difference is that you can send it without the person having to accept it.