I went to my first Renaissance fair in the early 1990s. It was such an extraordinary experience , that I went back the next year, and the year after that. I continued to go every year until the year I left the United States. I still maintain it is one of the things I miss most about the USA (not including Taco Bell).
The Renaissance fair is a celebration of the Renaissance period. There are musicians playing songs from the time period. The merchants wear period costumes, as well as some of the guests. There are plays from the period and jousting tournaments. Sometimes there are even tournaments with swords. There is always food from the time. Along with food, merchants sell beer and wine, jewelry and clothing from the period.
Part of the fun of the fair is dressing up and seeing everyone dressed up in costumes. There is usually a king and queen of the fair and they are always dressed in incredible costumes which are very well made replicas.
While a well made costume can cost hundreds of dollars, because of the expensive fabrics used, there are cheaper versions of different Renaissance costumes online.
Renaissance costumes can be very different in terms of styles for both men and women. Clothing during the period were specific to social classes. Each social class was defined by not only the style of dress but, most importantly, the fabrics.
During the Renaissance period, there were laws in place which prohibited peasants from wearing certain types of fabrics including satin, cotton, silk and velvet. Those fabrics were deemed acceptable for only the nobility, despite a peasant being able to afford the fabric. Peasants were relegated to leather, linen and wool mostly.
When choosing an adult Renaissance costume it is not necessary to adhere to the strict rules. However, if you wish more authenticity, you should keep them in mind. There are many shops which carry authentic replicas complete with fabric choices. These are mainly used by professional actors. There are some aficionados who have them for costumes. Otherwise, there are many lower cost, synthetic fiber costumes which you can buy online or at local costume shops.