First, after:
The conjunction “after” is used to link two sentences together: past simple and past perfect tense:
The conjunction “after” comes with the same usages as other conjunctions such as: when, as soon as, till, until.
The rule that governs them is:
past simple + after/ when/ as soon as/ because + past perfect
For example:
He went to buy a car as soon as he had got money.
After she had seen the ring, she accepted the marriage offer.
Note:
1. Till/ until also come before past perfect tense, but they are preceded by a negative past simple tense.
2. There are other ways for using “after” such as:
After + verb + (-ing) + past simple tense.
For example: After getting money, he went to buy a car.
After + noun + past simple
For example: After winning, he went to buy a car.
3. The word “having” can be used to give the same meaning as “after” as follows:
Having + P.P + past simple
For example: Having got money, he went to buy a car.
For example:
Marry did not apologize till she had realized her mistake.
Second, before:
The conjunction “before” is used to link two sentences together: past simple and past perfect tense:
The conjunction “before” comes with the same usages as other conjunctions such as: by the time and when.
The rule that governs them is:
past perfect + before/ by the time/ when + past simple
For example:
He had got money before he went to buy a car.
By the time she accepted the marriage offer, she had seen the ring.
Notes:
- “By the time” mainly comes at the beginning of the sentence unlike before/ after which are flexible when it comes to the position (in the beginning or in the middle of the sentence)
- The conjunction “when” can come with either tenses: past simple or past perfect but the meaning it gives in each time is different as the past perfect tense expresses the older action.
For example:
1. When we reached the market, the shops had closed.
2. When we had reached the market, the shops closed.
In the first example, the shops closed first. Then, they reached the market.
Whereas in the second example, they reached the market first. Then, the shops closed.
3. There are other ways for using “before” such as:
before + verb + (-ing) + past perfect tense.
For example: Before renting a house, we had tried to buy one.