LONG (Buy) position - is the process of buying an asset (Opening the position) at a low price, with the intent to resell the asset (Closing the position) at a higher price when the price of the asset increases.
Profit or Loss made in this case is the difference between the price at which you Opened the position (bought the assets) and the price at which you Closed the position (resold the assets)
Example of a LONG (Buy) position:
Trader opens a 1 BTC Long (Buy) position at the price of $4000. As stated previously 1:100 leverage allows trader to open this position using only 0.01 BTC of his own funds.
Let’s assume that later, the price of 1 BTC increases to $4100. Trader now closes the position.
Trader bought assets (Opened the position) at $4000 and sold them at $4100 (Closed the position), leaving him with $100 profit!
The 0.01 BTC Margin that was used to open this position will now be “unlocked” and available for trader to use again.
The $100 profit is now added to trader's balance and can be further used for trading or withdrawn.
As seen from the example, Long positions are better in uptrend markets, when price of an asset is increasing.