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||have||(= I’ve, etc.)||finished|
|he/she/it||has||(= he’s, etc.)||lost|
|we/you/they||have||(= we’ve, etc.)||done
The present perfect simple is have/has + past participle. The past participle often ends in –ed (finished/decided etc.), but many important verbs are irregular (lost/done/written etc.).