1. Most of the time you need main dictionary only. The main dictionary is built at Aspose. Main dictionary is for a particular language. English US dictionary is included in the installer, others are available from the Aspose.Spell download page.
To load main dictionary:
spell.LoadMainDictionary(MainDictionaryFileName);
2. Affix dictionary is an "additional" dictionary that might be pertinent to your project or your organization. It can be created manually by you, using a special tool included with the Aspose.Spell installer. I think these are not used too often.
3. Custom dictionary is just a collection of words that you can added to the Spell object at runtime to allow them to spell check correctly. Aspose.Spell does not store custom dictionary - it is up to you to store it. You can store it in a file or database. It is optional.
For more info see the demo source code included with the Aspose.Spell installer.
Roman Korchagin
Lead Developer,
Aspose Auckland Team