The main way to set the time in Chinese is through time specification (yesterday, next year…)…
Anyway, if we need to emphasize that action is finished (and distinguish it from other types of actions in the past), we use particle 了 <le> and place it right behind the verb.
了 <le>
我昨天喝了不少绿茶。
<Wǒ zuótiān hē le bù shǎo lǜchá.>
I yesterday to drink le not a little green tea.
YESTERDAY I DRANK QUITE A LOT OF CHINESE TEA.
我在中国买了很多中文书。
<Wǒ zài Zhōngguó mǎi le hěnduō Zhōngwén shū.>
I in China to buy le many Chinese books.
I HAVE BOUGHT MANY CHINESE BOOKS IN CHINA.
我给他说了，可是他不听。
<Wǒ gěi tā shuō le, kěshì tā bù tīng.>
I to him to say le, but he not to listen.
I TOLD HIM BUT HE WOULDN’T LISTEN.
我喝了这个茶，就要去上课。
<Wǒ hē le zhège chá, jiù yào qù shàngkè.>
I to drink le this tea, then yao to go to have a class.
AFTER I FINISH DRINKING THIS TEA, I WILL GO TO HAVE A CLASS.
If action just happened, 了 <le> is placed not after verb, but at the end of a sentense:
我买书了。
<Wǒ mǎi shū le.>
I to buy books le.
I (JUST) BOUGHT SOME BOOKS.
了 <le> (as an indicator of finished action) can´t be used with verbs, that can´t be considered as verbs of a single action, such as…
知道 <zhīdào> TO KNOW
想 <xiǎng> TO THINK
认识 <rènshi> TO KNOW (something, somebody)
是 <shì> TO BE
在 <zài> TO BE somewhere
If we want to say for instance “I used to know how to do this”, we just set it in the past using 以前 <yǐqián> (before):
我以前知道怎么做。
<Wǒ yǐqián zhīdào zěnme zuò.>
I before to know how to do (it).
I USED TO KNOW HOW TO DO IT BEFORE.
没有 <méiyǒu>
Negation (not just for finished action but for past in general) is created using 没(有) <méiyǒu>, without 了 <le>.
我昨天没(有)喝咖啡。
<Wǒ zuótiān méi(yǒu) hē kāfēi.>
I yesterday not to drink coffee.
I DIDN’T DRINK ANY COFFEE YESTERDAY.
他还没(有)问我。
<Tā hái méi(yǒu) wèn wǒ.>
He still not to ask I.
HE DIDN’T ASK ME YET.
你为什么没(有)给我说？
<Nǐ wèishéme méi(yǒu) gěi wǒ shuō?>
You why not to me to say?
WHY DIDN’T YOU TELL ME?
我没(有)买，因为太贵了。
<Wǒ méi(yǒu) mǎi, yīnwèi tài guì le.>
I not to buy, because (it) (to be) too expensive. (了<le> here is a part of a construction with 太 <tài>.)
I HAVEN’T BOUGHT IT, BECAUSE IT IS TOO EXPENSIVE.
For interrogation, we use the modul 有没有 <yǒumeiyou>, again without 了 <le>.
(There are also other ways, but this one is most common and the most simple.)
你以前有没有在中国工作？
<Nǐ yǐqián yǒuméiyǒu zài Zhōngguó gōngzuò?>
You before youmeiyou in China work?
HAVE YOU WORKED IN CHINA BEFORE?
你有没有收到我的短信？
<Nǐ yǒuméiyǒu shōudào wǒ de duǎnxìn?>
You youmeiyou to receive my SMS?
DID YOU RECEIVE MY MESSAGE?
他有没有给你说？
<Tā yǒuméiyǒu gěi nǐ shuō?>
He youmeiyou to you to tell?
DID HE TELL YOU?