The idea is to sell at the broker or exchange with the higher price and buy at the broker or exchange with the lower price. Once the market moves, you will have one profitable trade and one losing trade, but as you bought low and sold high, your winning trade should be slightly larger than your losing trade, which means you can close both positions for a riskless net profit.
But pure Arbitrage is actually quite rare. Why? Financial markets are set up in a way that discourages arbitrage from happening in the first place. Markets are designed so that securities are priced equally within all trading markets. They're said to be Arbitrage-free.
However the Crypto market is different because there are many independent exchanges and thus different prices on exchanges. This fact gives plenty of Arbitrage opportunities.
