Banks compete against other banks actually, and their trading desk. The same bank will even have positions that are against one another based on the trader working for the bank. But most now a days is algo trading for the big boys but there is still manual trading as well.
We as retail traders don’t actually even trade in the market. Our brokers handle our accounts we just speculate where we think the price is going. The broker either has someone on the other side of our trade or they take the other side and since most traders lose it’s usually a win for them over a series of trades.
Also why you want a regulated broker that also has a good reputation.