It is a polite and friendly way to respond to a request or offer.
Here are some examples of how it can be used:
* "Would you like a cup of coffee?" "Oui, avec plaisir!" (Yes, with pleasure!)
* "Thank you for your help!" "De rien, avec plaisir." (You're welcome, with pleasure.)
* "Can you open the door?" "Avec plaisir." (With pleasure.)
Essentially, "avec plaisir" conveys that you are happy to do something or that you are grateful for something someone has done for you.