The best way to learn how to use TortoiseCVS is to play with it. Start by installing TortoiseCVS.

If you are new to CVS start following along with Basic Usage of TortoiseCVS.

Once you've learned the ropes check out the advanced features in Advanced Usage of TortoiseCVS.

For pure reference, the chapters Command Reference for TortoiseCVS and Dialog Reference for TortoiseCVS will help you get the most out of TortoiseCVS.

And finally check out Articles, Tips and Tricks for a complete and enjoyable version control experience.