When you get a bunch of people together in a party setting, a good game can get people involved in the party. Some card games are a great way to help people to get to know each other; others are great activities to have as the main event for the party.
Ice Breaker Games
There are a few very simple games you can play with a deck of cards, such as "Indian Forehead," a game where players draw a card at random and stick it to their forehead. Players then try to figure out what their card is by speaking with other players. There is another, similar game called "Mafia," in which players get a role from the card they draw. The players then try to figure out who is who, based on a series of instructions.
Set up a poker table with snacks and drinks, then gather a bunch of players who are all interested in a game like poker, and you have a party. Start with a cheap buy-in and play the round. "Texas Hold 'em" is a good variety of poker to begin with, although you may find other styles that work as well. You will likely have some new players in the game, so treat them with some respect and teach them a few tricks.
With a deck of cards designed for a certain game, there are more games you can play. If you have "Fluxx," or "Apples to Apples," these are great games involving a wide number of people which can be played. In "Fluxx," a player draws a card and plays a card from their hand of three. The card he plays will change the rules of the game. In "Apples to Apples," a judging player selects a green card with an adjective. Players select the red card with the noun they feel most applies, for the judge to select the most apt.
These games are only for adults legally able to purchase and consume alcohol in their state. With a deck of cards, you can play a number of different games, like "Kings," in which the deck is spread out at random on a table, and players draw the cards one at a time. Each card has a rule associated with it, such as the 3, which means "me": The player who draws a 3, takes a drink. The rules may vary slightly in different areas, but the gameplay is roughly the same.