How do form the past and past participle?

Answer 1

You form the past tense of regular verbs by adding -ed. The past tense of regular verbs is also the same form used for the past participle.

Irregular verbs don't add -ed to form the past tense but rather the word changes. For example 'eat' becomes 'ate'.

and

the past participle for irregular verbs is often a different word (or it can be the same as the past)

for example:

eat / ate /eaten - eaten is the past participle.

dig / dug / dug - dug is past participle.

run / ran / run - run is the past participle

Because they are irregular verbs there is no rule how to form the PP you just have to learn them.