This 30-day, fully functional trial gives you plenty of time to determine whether it will work for you. There are also other programs that do similar things, including systracker and WorkTime, which I haven't looked at yet.
This program's setup is much like a spreadsheet program's. In each file (called a Project), tabs along the top (Time Sheets) let you keep track of multiple aspects of one project. Or, you can use one timesheet per small project. You can manually enter start and stop times or use the "start time" and "stop time" commands to have the program automatically enter them. A system tray icon also makes this easy.
In actual use, the program can get a bit unintuitive. And I did have trouble with two features: entering a rate (in dollars per hour) and formatting cells properly (which requires precision). Entering a rate appears to be a time-consuming task of defining each time slot and its particular rate. And when I made a mistake in formatting, the error messages weren't particularly helpful (There's no way to easily fix the problem in "row 5" when the rows aren't numbered.). You also must tell the program to calculate the data -- something it should do automatically.