These two words--before and after--are often used in daily life. But their usages in Chinese are different from English. Let's look at the words here:  

Before: yǐ qián, 以前

After: yǐ hòu, 以后

The first difference here is the position of these two words. In English, it's "before/after doing something". But in Chinese, it's "doing something before/after". They're the same meaning but the position is reversd . For example:

(1) Before going home = huí jiā yǐ qián (huí jiā=go home; yǐ qián=before)

(2) After going home = huí jiā yǐ hòu (yǐ hòu=after)

Chinese learners in Britain and America need to get used to the reverse of the position, especially while listening. 

Here is the other difference. In English, the phrase with before and after could be at the beginning or in the end of a sentence. But in Chinese, the phrase only should be at the beginning of a sentence. For example:

(1) I will go to supermarket before I go home =Before going home, I will go to supermarket.

     Huí jiā yǐ qián, wǒ qù chāo shì 。 (回家以前，我去超市。)

    (huí jiāg=o home; yǐ qián=before; wǒ=I; qù=to go; chāo shì=supermarket)  

(2) I will go home after I go shopping =After going shopping , I will go home.

     Mǎi dōngxī yǐ hòu, wǒ huí jiā 。(买东西以后，我回家。)

     (mǎi dōnɡ xi=shopping; yǐ hòu=after; wǒ=I; huí jiā=go home)  

So here are the sentece strctures:

(1) Action A + yǐ qián,  Subject + action B.

        It means: Before doing action A, I do action B.

(2) Action A + yǐ hòu,  Subject + action B.

       It means: After doing action A, I do action B. 

Some final words: learning language is not to only memorize the rules but to communicate with local people. "OK, I understand" is not enough. Lots of practice is necessary. Remember, practice makes perfect. If you have any questions, feel free to leave me a message. I will reply as soon as possible.