A) Study this example situation : Tom is looking for his key.He can't find it . He has lost his key . He has lost his key.He lost it recently, and he still doesn't have it . Have/has lost is the present perfect simple : I/we/they/you --> have(=I've etc.) ---> finished , lost , done , been , etc. He/she/it --> has ( ==he's etc.) ---> finished , lost , done , been , etc. ----- B)When we say that ' something has happened', this is usually new information - When we use the present perfect , there is a connection with now . The action is in the past has aresult now ! C) You can use the present perfect with just , already , and yet Just = a short time ago - ' Are you hungry? ' ' No, I've just had lunch ' -Hello.Have you just arrived ? We use already to say that something happened sooner than expected : - ' Don't forget to send the letter ' ' I've already sent it' - ' What time is Mark leaving ? ' ' He's already gone ' Yet = until now . Yet shows that speaker is expecting something to happen . Use yet only in questions and negative sentences : - Has is stopped raining yet ? - I've written the letter , but I haven't sent it yet That's all. They had token from English Grammer in Use. THAT İSN'T COPY-PASTE . I have answer I will send them after a little time . Have a nice day .