what does going long & going short mean in trading?

Going Long

Going long means you think that the price of an instrument will rise upwards, so you are buying low at the current price in order to sell at a higher price and exit the market with your profit. When price is increasing, the candles on the chart appear taller and taller hence the word "long" is used.

Going Short

Going short means, you think that the price of an instrument will sink/fall to the bottom, so you are selling high at the current price in order to buy at a lower price and exit the market with your profit. When price is falling, the candles on the chart appear to keep sinking downward thus giving a visual impression of shortening or a gradual decrease in height.

Going short means, you want to enter the market by clicking on the "buy" button (it is ideal to buy when price is rising) while going short means you want to enter the market by clicking on the "sell" button (it is ideal to sell when price is falling).