The words since and for both deal with time. The two words are related to a duration or time period. Both words are prepositions (although since is also an adverb and a conjunction).
SInce和for的使用都與時(shí)間有關(guān)。這兩個(gè)詞都與時(shí)間段有關(guān)。兩個(gè)詞都是介詞（但since也是副詞和連詞）。

For example,
例如，

I have been teaching English for 10 years.
我教英語(yǔ)已經(jīng)10年了。

or
或

I have been teaching English since 2007.
我從2007起開(kāi)始教英語(yǔ)。

FOR:

The word for also sounds like the number 4. This reminds me of mathematics.
For聽(tīng)起來(lái)也像是數(shù)字4的發(fā)音。這讓我想起了數(shù)學(xué)。

When you do the math (or calculate the amount of time) for the person then you use FOR.
當(dāng)你為某人計(jì)算數(shù)學(xué)題目（或計(jì)算時(shí)間）時(shí)，則使用FOR。

For example:
例如:

I have been waiting for 10 minutes.
我已經(jīng)等了10分鐘了。

She has lived in the United States for 20 years.
她在美國(guó)住了20年。

He has been raising his hand for an hour.
他已經(jīng)舉起了一個(gè)小時(shí)的手。

SINCE
:

Since generally refers to the beginning of some period.
Since一般指的是指某一時(shí)期的開(kāi)始

Let's look at some examples:
讓我們看一些例子：

She has been working out since 2:15pm.
她從下午2:15開(kāi)始一直在工作。

They have been studying medicine since 2016.
他們從2016年以來(lái)就一直在學(xué)醫(yī)。

I have been living here since 2013.
我從2013年以來(lái)一直住在這里。

I haven't seen Sarah since Friday.
自從星期五以來(lái)我就沒(méi)見(jiàn)過(guò)莎拉。

One last thing about since.
關(guān)于since的最后一點(diǎn)。

If you use the sentence, "It has been… (years or some time) then you MUST use since when using Present Perfect Verb Tense.
如果使用這個(gè)句子："It has been…（某年或某個(gè)時(shí)間）時(shí)，因?yàn)樵摼錇楝F(xiàn)在完成時(shí)態(tài)時(shí)，所以必須使用since。

For example,
例如：

It has been 5 years since I quit smoking.
我戒煙已經(jīng)5年了。

Next month, it will have been 4 years since I have been living in Brazil.
到下個(gè)月，我已經(jīng)住在巴西4年了。