One of the first challenges you may come across in doing family history and dealing with koseki is reading the dates. The following are two fairly helpful charts for this.
First, a conversion chart for the Japanese calendar system. Traditionally, the year is recorded as the year in the reign of a particular emporer. For example, I was born in Showa 58, or 1983. The Koseki will only show the Japanese year, not the western year, but you can look it up here (click to view larger):
Another problem is that koseki may use antiquated characters. I'll include some additional charts for other kanji in other posts, but for now here is a chart that shows various written forms of each number.