1. Such verbs as learn, spoil, burn, dream, smell, spill, leap, and others, can be either irregular (learnt, spoilt, etc.) or regular (learned, spoiled, etc.). Although in British English both variants can be used there is a tendency to use irregular forms. However, in American English regular forms with the –ed ending are used almost all the time. Compare:
Infinitive Past Participle (BrE) Past Participle (AmE)
bust bust busted
get got gotten
lean leant/leaned leaned
learn learnt/learned learned
saw sawn sawn/sawed
smell smelt smelled/smelt
spill spilled/spilt spilt etc.
2. The verb fit has usually a past participle form of fitted in British English but fit in American English (however, when the word is used in the sense “to tailor” then fitted is also used in American English).
3. In American English the verb get is quite often used in the meaning of “have” in the collocation have got (in British English simply have is used). In this case past participle will be have got (even in American English). Compare:
British English American English
I have a ticket. I’ve got a ticket.
I have had this ticket since Monday. I have got this ticket since Monday.
4. In American English many irregular verbs allow to mix their past participle and past simple, while in British English it happens rarely. For instance, spring-sprang-sprung (BrE), spring-sprang/sprung-sprung (AmE).
There are some further differences, but they are minor, quite complicated and used locally or specifically by some groups of people; therefore, not very important to your TOEFL preparation.