Extend vs Include

Hi… I’m very confused with the diference between <> and <> (Talking about use case)

It is posible for you answer this question ?

When I must use one or another ?

Very tks

A Use case like

  A ----- <<includes>> ----> B <----<<extends>>----C

In an activity diagram it means
A1 -> A2 -> A3 -> (B) -> A4 -> A5
during the process of A the B part is executed

B1 -> B2 -> (check true) -> B3
…(check false) -> ©
during processing B it can happen that also C is executed (e.g. if a certain condition is fullfilled) but B can also be executed without C