Long position is a position established with an expectation that the price of an asset will go up.
In certain markets, to go Long (i.e. to open a long position), you may need to actually purchase an asset. For example, you would buy a stock on stock market or you would buy a digital asset on a cryptocurrency exchange.
There are other instruments, however, which allow you to hold an asset without actually owning one. These instruments are broadly called derivatives. In the case of a derivative, you are exposed to the price fluctuations of an underlying asset, without actually owning it. If you have Long position, you are hoping that the price will go up.
Regardless of an instrument, with Long position, if the price of that asset does go up, you would close it with a profit. If, on the other hand, the price goes down, you’ll get a loss.
To solidify your understanding and to go through a specific example of Long, visit this article.