By sending a kiss you show that you're interested in a person and that you wouldn't mind to talk some day. So it's an additional way to say Hi or to show affection.
You can find him or her in search results and press Send a kiss link. In a new window choose a kiss that is most matching the occasion and press Send.
At your homepage there's a Statistics section where you can see users who sent you a kiss. Just click the link for the option: users who sent me a kiss to see users list with kisses they sent.
Yes. You can see it in your homepage stats section where there's a link for "users I sent a kiss". Click it to see a list of users with kisses you sent to them.
All members can send Kisses for free. There's no limitation for sending a kiss. Only if you're in someone's Black list your kisses won't be delivered.