A call is the right to buy at the strike price; a put is the right to sell. The buyer pays a premium for that right and can lose no more than it. The seller collects the premium and takes on the obligation, with far larger potential losses.
The premium has two parts. Intrinsic value is what the option is worth if exercised now; time value is everything else, and it decays towards zero as expiry approaches. That decay is why a correct view on direction can still lose money if it takes too long to play out.
Implied volatility is the market’s forecast of future movement priced into the premium, and it usually matters more than direction. Buying options before an earnings release, when implied volatility is elevated, often loses even when the stock moves the right way, because the volatility premium collapses the moment the news is out.