Countable:
* When referring to specific individuals: "I have three close friends."
* When discussing a specific group: "The friends I made in college are still close."
Uncountable:
* When referring to the general concept of friendship: "Friendship is a valuable thing."
* When using "friends" to describe a group of people collectively: "The restaurant was filled with friends enjoying a meal."
In summary:
* Countable when referring to specific individuals or groups.
* Uncountable when referring to the concept of friendship or a collective group of people.