There are two ways that most runners keep records about their runs.
- Special software to keep a diary or log of their runs
- A blog of their runs
DiariesThe use of software that creates and maintains a log of your runs has one big advantage: you are less likely to forget to record particular data about your runs. There is one disadvantage, though, of using diary-software: you have to have the discipline to enter data about each run; it is easy to neglect the diary for a few days, and you may not remember some of the data that should be preserved. I've been told by friends that their diaries have data displayed in charts that make the data easy to understand and easy to compare from day to day and week to week. Some diaries allow you to import data from a GPS and/or a heart-rate monitor.
I haven't looked into this, but I expect there are programs that you install on your computer to provide a diary of your runs. However, most of the runners I know who keep a diary use online services provided by web sites. Some of the online diaries are free. A little searching of the Internet will give you links to online running diaries.