I used to do it for a living. Great fun when you're using someone else's money i.e. I worked for an International Bank, but you have to be realistic and remember that you're playing for real and you could lose a hell of a lot of money. FX spot markets can move very fast and usually doi when news is out that affects one or other currency. The biggest downside is "paying away the spread" and is where most of the big players clean up as they just quote and get hit by other banks/companies all day long and therefore just make the spread.
For example GBP/USD is quoted at 1.7425-1.7430 you buy GBP at 1.7430 and sell GBP at 1.7425, whereas if other people "hit" your quotes, they BUY at 1.7430, i.e. you sell and they sell at 1.7425, i.e. you buy. If the amount is GBP1,000,000.00 and someone trades off your quotes, you have then sold GBP1,000,000.00 @ 1.7430 and received USD1,743,000.00, then on the other side you have bought GBP1,000,000.00 and sold USD1,742,500.00. This means that you have made 5 points profit on GBP1,000,000.00, i.e. USD500.00. Alternatively, you buy at GBP1,000,000.00 at 1.7430 and then sell at 1.7425, you lose USD500.00
Now if we put a 10 point market move into the equation...
You buy GBP1,000,000.00 at 1.7430 and then the market moves to 1.7435-1.7440. You now sell GBP1,000,000.00 at 1.7435 and you have ade USD500.00 profit. However, if the market moves down 10 points to 1.7415-1.7420 then you sell at 1.7415 and lose USD1,500.00
If you know nothing about FX, then my advice is steer well clear and leave it alone. If you have some money you can afford to lose and want to give it a go, then learn as much as you can first, read everything and keep up to date with the news in the countries/regions where the currencies are from. When you have an open position, i.e. you have bought or sold and have yet to close it out, you will be monitoring it 24 hours a day - do you really want that hassle ?