Real fruit is best added after primary fermentation is complete. This helps to keep some of the fruit aroma from being driven off with the mass of CO2 created. Most people put them in a secondary and rack the primary over it but it is possible to just add to the Primary.
Canned peaches or peach purée can go straight in. Fresh whole peaches should soak a couple minutes in sanitizer before freezing. Give them a thourough rubbing under the sanitizer or the fuzz will create air pockets and unsanitized surface area. After freezing, thaw, soak in sanitizer, then slice with a sanitized knife. You can toss that straight in (not any fuzz) or soak in vodka for 1-7 days before pitching fruit and vodka in. Some people prefer to run through a blender with a little vodka. Some people blender and then heat to 180 for 10 minutes, cool and pitch. The possibilities and combinations are practically endless.