Are you saying in a specific opening, or in general?
If you are talking in general, here are a number of items I would highly recommend. All of them deal with various forms of pawn structure, each of which have their own key squares. For example, in the case of isolated pawns, the square in front of the isolated pawn is always a key square. See the following. I would suggest them in the order listed (not rank best to worse, the last 2 are excellent, but order in which you should read them based on difficulty):
https://www.amazon.com/Inner-Game-Chess-How-Calculate-ebook/dp/B00WL76LTE/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1468252615&sr=1-1&keywords=Inner+game+of+Chess
https://www.amazon.com/Understanding-Pawn-Chess-Drazen-Marovic-ebook/dp/B00F289BU0/ref=sr_1_2?ie=UTF8&qid=1468252384&sr=8-2&keywords=Pawn+play+in+chess
https://www.amazon.com/Power-Pawns-Structure-Fundamentals-Post-beginners-ebook/dp/B01FIT2YQA/ref=pd_sim_351_4?ie=UTF8&dpID=51k-u9KXhXL&dpSrc=sims&preST=_OU01_AC_UL320_SR232%2C320_&psc=1&refRID=40MD8RNCZPQ1J102P2ZD
https://www.amazon.com/Techniques-Positional-Play-Practical-Methods-ebook/dp/B00IIWM64A/ref=pd_sim_351_6?ie=UTF8&dpID=41lDxDwp6tL&dpSrc=sims&preST=_OU01_AC_UL320_SR232%2C320_&psc=1&refRID=J0KPNTAYZMZ8A48WTYY3
https://www.amazon.com/Improve-Your-Chess-Pattern-Recognition-ebook/dp/B00QFVZHKG/ref=pd_sim_351_6?ie=UTF8&dpID=51MN0pkC5IL&dpSrc=sims&preST=_OU01_AC_UL320_SR226%2C320_&psc=1&refRID=DRK8F42TX51HYZN84P1N
https://www.amazon.com/Train-Your-Chess-Pattern-Recognition-ebook/dp/B01HFM9NZI/ref=pd_sim_351_1?ie=UTF8&dpID=51e66VBVoqL&dpSrc=sims&preST=_OU01_AC_UL320_SR232%2C320_&psc=1&refRID=0ZM8BFX9A42MNTJTCZFT
I can't find anything on this online. Can you guys please help me? Thank you.
I'd really appreciate your help. Thank you soooooo much.