English verbs are either regular or irregular. We call a verb regular when we add ed (wanted, looked) or sometimes just d (created, loved) to form what are called the simple past tense and the past participle (see third and fourth paragraphs below). A regular verb's simple past tense and past participle are always identical.
Not so with irregular verbs. They form the simple past tense and the past participle in any number of unpredictable ways. Some irregular verbs, like let, shut, and spread, never change, whether present or past. Others, like feel and teach, become modified versions of themselves (felt, taught) to form both the past tense and the past participle. Still others, like break and sing, change to form the past tense (broke, sang) and change again to form the past participle (broken, sung). And then there are a few really weird ones, like go: its past participle (gone) is recognizable enough, but its simple past tense is a strange new word (went).
Let's get back to the irregular verb break. The simple past tense is broke, which we use in sentences like I broke your dish. We use the past participle, broken, to form compound verbs in sentences like I have broken your dish. The compound verb have broken is so called because we've added a helping verb (have) to the main verb's past participle (broken). Be careful never to add a helping verb to the simple past form of an irregular verb—I have broke your dish is regarded as uneducated usage.
The past participle of an irregular verb can also function as an adjective: a broken dish. But the simple past form, if it differs from the participle, cannot function as an adjective: a broke dish is substandard English.
There are far fewer irregular verbs than regular ones, but we use them all the time. "The ten commonest verbs in English (be, have, do, say, make, go, take, come, see, and get) are all irregular," notes Steven Pinker, an American experimental psychologist and linguist, "and about 70% of the time we use a verb, it is an irregular verb."
Proper use of irregular verbs requires old-fashioned memorization—there are no secret formulas or shortcuts. This is why these words can create havoc for conscientious speakers of English.