Here are the rules:
1. Regular verbs ending in a silent e take /-d/ in the simple past and past participle:
Example:
close=closed
2. Regular verbs ending in a vowel + y take /-ed/ in the simple past and past participle:
Example:
play=played
3. Regular verbs ending in a consonant + y take /-ied/ in the simple past and past participle (the y becomes an i followed by /-ed/)
Example:
marry=married
4. All the other regular vebs take /-ed/ in the simple past and past participle.
Example:
visit=visited