Eventually, someone you know will get married. It's just about inevitable. If it's you, your bride will probably have already figured out what you will wear. It is harder, though, if you are a guest. Formal weddings, afternoon weddings, casual weddings.... What does it all mean?
Here's the lowdown:
White tie: This is as formal as it ever gets. It's called white tie because....you wear a white bowtie with the outfit. It consists of a white wing collar pique shirt, white pique vest and tie, classic black trousers with the formal satin stripe, traditional black tailcoat just covering the vest, and black patent shoes.

Black tie: This is the most common of formal type wear. It is your regular black tuxedo with a cummerbund or vest, a tie ( you have a few choices here: a bow tie, either black or matching the vest or cummerbund, or a regular tie, matching or accenting the vest) and black patent shoes. The cummerbund should be worn with the pleats facing up.

Semi-formal: Go for your good suit. Black, grey or navy are your best bets. Best shoes are black oxfords, black loafers. Nice tie required. Handkerchief in the breast pocket is optional.

Casual: Here's where you get to dress relatively normally. There are a couple of options. They all start with dress slacks, usually grey or blue, but they can be black or brown. Also a nice button down shirt. To top it off, a blazer or nice sweater. The tie is optional.