What is the difference between 了 and 过 when used after a verb?

Both particles are used to signify the past tense of a verb, but they signify different types of past tense (which we don't really have in English). 过 is used when to convey the action has been experienced, such as '"I've seen that film twice" or "I've been to China" (and is more like the imperfect tense in, say, French) 了 is used to just convey completion, such as "I've finished eating" or "I went to the cinema".