An etymological dictionary has the roots of words. The best is the Oxford English Dictionary, but it is behind a paywall. However, there are free ones online. Just google "etymology of X." As for verb classes, google Old English Verb Classes. They should give you examples of modern words from each class. Each class formed its past and past participle in a different way. The largest class was the one that added a d or t sound at the end of the word, and we call those "regular" verbs today.