In the River Plate it is extremely common for people to kiss. Kissing each other is usually more popular than shaking hands (among your coworkers, friends even between teachers and students). Shaking hands is rather a formal way of salutation, and you only use it in very specific occasions, like official appointments, meetings or gatherings. Remember to say the equivalent of "hi" in Spanish always before kissing or shaking hands with the other person, so never forget to say a explicit "Hola". Unlike in many other cultures, you are expected to say hi "hola" and physically greet the person or at least to always say hello.

The same ritual happens when you leave the person: you need to say goodbye and kiss or shake hands always. A "chau" or "hasta luego" (in informal way just 'ta luego) is required. It is considered very impolite and rude not to leave a place or group of people without saying the Spanish equivalent of goodbye.

Kissing in Uruguay means to give someone only one kiss on the cheek. This is important to tell because in Brazil people kiss twice. And in Hollywood they've perfected the air kiss. Here, it's lips on cheek. An air kiss would be rude.

Regarding salutation of genders:

Bewteen two men: If you know the person (this means you had at least met him once or twice before) you are expected to kiss on the cheek. Remember, one kiss only. You may hug the person as well if it is a person of your next-of-kin and you have special appreciation to him or you have not seen him in a long time.

Between two women: A kiss is the most common. Rarely you see two women shaking hands.

Between a man and a women: A kiss is the most common.

If you want to get acquainted with locals you should follow these salutation rules.

 Even while waiting at the membership desk of the local gym a young boy of about 12 years walked in. Hew saw a friend. Another boy his age. The two boys kissed then he kissed his friends father. Perfectly natural behavior here.