Dirac delta function and electrostatic boundary conditions

[asdf1]

Help on "Introduction to Electrodynamics 3rd edition by David J. Griffiths"

I'm studying that book right now, but I'm having a hard time understanding...
Can someone explain what a dirac delta function is and how to use it?
I also don't understand the what is the electrostatic boundary conditions are on page 87...

 

[quasar987]

have you read the few pages about it in the beginning of the book? If you're still unsatisfied with this, try

https://www.physicsforums.com/showthread.php?t=73447&highlight=dirac+delta

 

[asdf1]

thank you~