Can someone educate me to what how the PCV valve works and it's function?

[Evans Ward]

Need the basics and 101 course on how the TR PCV valve works. I do know it's a check valve and that it only flows in one direction. I discovered mine was flowing both directions and noticed quite a bit of oil on the back of the intake. Chasing an oil leak so hoping this was it. I did have a correct NOS TR AC-Delco PCV valve to replace it. Educate me please! Thanks!

 

[Junior Samples]

some information on link i found

http://www.supersixmotorsports.com/pdf/PCVBypass.pdf