Here are some commonly-misused words. They look quite similar, but they are not the same.
loose – adjective. The opposite of tight. “My pants are loose because I have lost weight.”
lose – verb. You lose something when you no longer know where it is, or when you can’t use a skill any more. “Don’t lose your lottery ticket! You will need it if you win.” OR “If I don’t practice my English, I will lose my skills.”
loser – noun. The person who loses. Note that it is an insult. “James is the winner, and everyone else is a loser.”
loss – noun. The amount of money that you spent in order to gain a lesser amount; the opposite of profit. “We received $100, but we spent $130. Our loss for this deal is $30.”
lost – adjective. Use this to describe something that you lose. “I can’t find my glasses; they are lost.”