price you are out.

Long simply means you are betting what you are buying will go higher.

but there are inverse etf like dxd. if you long dxd it meaning you bet dow jones will go lower. so you long dxd to short the market.
So if you short dxd, skf, meaning you are betting market to go up.

Short simply means you are betting what you are buying will go down. You sell teh borrowed shares at current price. Then wait for the price to drop so that you can buy it back at cheaper price. or you Buy dxd etc to bet teh market to go down then you can sell dxd at higher price.