lose (Verb), to lose something;
e.g., I lose money every time we go to Las Vegas!
e.g., I found a set of keys. Did you lose yours?
lost (Past Verb and Past Participle);
e.g., I lost my keys.
e.g., I have lost my keys before.
BE lost (Adjective)
e.g., I am lost. I need a map!
e.g., I don't understand what the teacher is saying. I'm totally lost!
loss (Noun), a person or thing that you have lost;
e.g., Our house burned down and we didn't have fire insurance, so we had to cover the finanical loss ourselves.
e.g., Sam: My Mother died yesterday. Max: I'm sorry for your loss.