Your caterer or licensed liquor dealer will be responsible for setting up the bar at your reception. You must determine how hard the liquor should be as well as if you prefer your guests to pay for drinks themselves.
A cash bar requires the guest to pay for their drinks. It's usually shunned upon because it isn't proper to ask your "guests" to pay for anything regarding your wedding reception. Installing a cash bar will usually save you money since your guests are footing the bill. Guests tend to consume alcohol less frequently when it isn't free.
This is a basic bar with all the works. You have your hard liquor for mixing drinks, beer, and soft drinks. Your guests will be comfortable with this setting because it functions similar to a normal bar.
A limited bar will set boundaries on what will be served and in what moderation. You may want to provide a small limited bar with strong alcohol kept to a minimum. On the other hand, you may want to remove the hard alcohol all together and just go with serving light wine and fruit punch.