The currency exchange system was an approved means of trading Robux to tickets, and vice versa. To access this feature, you had to click the"Money" link on your user page, followed by the "Trade Currency" tab.
You would be taken to a Currency Exchange window. On the far right you would see a listing of all the people looking to trade either Robux or Tickets, and at what exchange rate they're offering.
A ticket ratio of "10 @ 2:1", for example, means that someone was selling 10 tickets and was looking to buy 5 ROBUX because she/he is buying them at a ratio of 2 to 1. In other words, 10 divided by 2 is 5.
A Robux ratio of "5,000 @ 1:5", for example, means that someone was selling 5000 ROBUX, and was looking to buy 25,000 tickets, because she/he is buying them at a ratio of 1 to 5. In other words, 5000 multiplied by 5 is 25,000.
Market order vs Limit order
A market order is a buy or sell order to be executed immediately at current market prices. As long as there are willing sellers and buyers, a market order will be filled.
A limit order is an order to buy at no more (or sell at no less) than a specific price. This gives you some control over the price at which the trade is executed, but may prevent the order from being executed.
Which order should you choose? That depends. A limit order gives you a little bit more control over the price you wish to trade at. However, you have to be very careful with your math -- one typo can cost you lots of tickets or Robux. A market order gives you less control over prices, but transactions are quick and efficient.
My Open ROBUX< Positions shows the as of yet incomplete trades you have trading ROBUX for tickets. You can't cancel these trades anymore, since the system got discontinued.
An example would be:
1000 ROBUX @ 1:10 1,000
Offers 1000 of your Robux for 10,000 tickets at the rate of 1:10 (i.e., 10 tickets for every 1 Robuck). 1000 Robux have yet to be traded.
An example would be:
5,000 tickets @ 2:1 5,000
Offers 5000 of your Tickets for 2500 Robux at the rate of 2:1 (i.e., you are hoping to get 1 Robuck for every 2 tickets.) 5,000 of your tickets have yet to be traded.
My Trade History
Your trade history used to show completed trades you have made.
A split trade will allow your trade to be broken up into smaller pieces among more than one buyer, which may allow your transaction to go through the exchange quicker.
As of April 14th, 2016, tickets were discontinued by ROBLOX, and currency exchange have since then became obsolete.