Say you thought TSLA was going to fall below $200 and you bought a put at that strike costing you $1250. As the underlying falls towards the strike price, the put contract you bought will increase in value. You will need to Sell to Close your put to capture the profit.

At expiration:

1. Underlying is ITM (below strike), the option is automatically exercised and you will receive profit
2. Underlying is OTM (above strike), the option expires worthless and you lose all your $1250. Or you sell earlier for a loss.

You are making a bet on what direction the underlying price will go. If you bet right, then you "lose less" from holding the shares due to the profit received from your option play.