A long call is simply the purchase of one call option.
Risk / Reward
Maximum Loss: Limited to the premium paid up front for the option.
Maximum Gain: Unlimited as the market rallies.
When to use: When you are bullish on market direction and also bullish on market volatility.
A long call option is the simplest way to benefit if you believe that the market will make an upward move and is the most common choice among first time investors.
Being long a call option means that you will benefit if the stock/future rallies, however, your risk is limited on the downside if the market makes a correction.
From the above graph you can see that if the stock/future is below the strike price at expiration, your only loss will be the premium paid for the option. Even if the stock goes into liquidation, you will never lose more than the option premium that you paid initially at the trade date.
Not only will your losses be limited on the downside, you will still benefit infinitely if the market stages a strong rally. A long call has unlimited profit potential on the upside.