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The trade will execute between 50 and 55 but not higher. In high volatility the trade might not be executed at 50 but at a higher value. The limit caps losses at 55. Also since this is a GTC order you might consider price changes overnight. If the closing price is 49 no trade is made. If the market opens and shares are trading at 53, for example, trade will execute at 53.
A stop order is basically an instruction to start trading when a specific condition is met. For example, if you had a long position on 100 shares and the stop instruction was “sell $30”, if the price fell below $30 you would sell as mnay shares as possible. This in effect would “stop” your losses from being higher if the price was sharply declining.
On the other hand, a limit order is an execution instruction which assigns a certain threshold below or above which trading will not happen. Using the previous example, if your limit instruction was “sell limit $30”, then no no sell orders would be placed if the share price went below $30. Crucially, though if the share price fell below $30 this would not stop losses as you still would have a position on the shares and would continue assuming losses.
Hope that helps.