There are broadly two types of fonts namely "Serif" and "Sans-Serif". You can check out more details about them on their wikipedia pages at
- Serif Fonts
- Sans-Serif Fonts
Although you are free to experiment, the general wisdom is that serif fonts are good for printing, while sans-serif fonts are good for screen/web viewing. So, while preparing the book for Pothi.com's POD service, you would generally want to use a Serif Font for body text. Sans Serif font can be used for headings, titles etc. But for main body text, use a serif font.