The verbs ending in -ed are Past Simple. They're used to narrate complete events in the past. e.g. I spilled the milk this morning.
The other verbs you mentioned (spilt, learnt, spoilt) are Past Participles. They're used to make 'perfect' tenses -=e.g. Present Perfect (I have spilt the milk) and Past Perfect (The class had already learnt addition before they started learning subtraction).
All verbs have 3 main forms: Present, Past Simple and Past Participle. In irregular verbs, there are 3 different forms:
swim, swam, swum
eat, ate, eaten
ring, rang rung etc
For regular verbs the Past Simple and Past Participle are the same:
open, opened, opened
finish, finished, finished
Pass, passed, passed is another example of the latter case where the 2nd and 3rd forms are the same - it doesn't fit with the other examples you've given.