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).
I have been teaching English for 10 years.
I have been teaching English since 2007.
The word for also sounds like the number 4. This reminds me of mathematics.
When you do the math (or calculate the amount of time) for the person then you use FOR.
I have been waiting for 10 minutes.
She has lived in the United States for 20 years.
He has been raising his hand for an hour.
Since generally refers to the beginning of some period.
Let's look at some examples:
She has been working out since 2:15pm.
They have been studying medicine since 2016.
I have been living here since 2013.
I haven't seen Sarah since Friday.
One last thing about since.
If you use the sentence, "It has been… (years or some time) then you MUST use since when using Present Perfect Verb Tense.
如果使用这个句子："It has been…（某年或某个时间）时，因为该句为现在完成时态时，所以必须使用since。
It has been 5 years since I quit smoking.
Next month, it will have been 4 years since I have been living in Brazil.