hello Marian~ when you form a sentence in the past tense, you can add the word "le" after the verb, for example: —zuo tian ni qu na le me? 昨天你去了吗？ (did you go there yesterday?) —shi de, wo qu le. 是的，我去了。 (yes, i did) just remember, generally we locate "le" after the verb to form a past tense sentence. but if one noun or pronoun is after the verb, there're two situations then: 1.v. + n./p.+ le 2.v. + le + n./p. both them are right!! for example: "zuo tian wo jian dao ta le" 昨天我见到他了。 or "zuo tian wo jian dao le ta" 昨天我见到他了。 (i met him yesterday.) sometimes, we also form a present perfect tense with "le" too,for example: —ni chi guo fan le ma? 你吃过饭了吗？ (have you eaten your diet?) btw, when Chinese people meet each other, we always greet with this question~ XD —chi le. (yes,i have.) maybe my answer is not so perfect,but i hope it could help you~ XD

add a "了(le)"under the verb ,for example: 你看了吗？（ni kan le ma?)——我看了。(wo kan le.)

add a "了"under the verb is OK

The simplest way is to add the "了" right after the verb. For example: I eat rice (我吃饭). "eat" is a verb, adding "了" after the verb, thus became 我吃了饭 -past tense.