Further to Sampeys reading homework that he gave you....

Basically the way CAT works in its simple configuration is to have CAT running 24/7 on a single exchange using one of the API's that can be purchased and then selecting a currency pair to trade from the market that is available from the exchange you chosen. Later on, you can add additional APIs to start trading on multiple markets at the same time.
At this stage, CAT does not allow you to trade between exchanges but we can trade multiple currency pairs from the same exchange.
This includes the ability to run multiple instances of CAT (in different folders within your pc) using the same exchange API that you purchased.
This allows you to run very complex configurations which I am sure some traders on here do.

As far as actually using CAT to trade and make a profit, all you need to do is select the currency pair, determine what min profit gain you want and then CAT will place order(s) onto the market and then continually monitors price movements in order to make the required profit. Once CAT exits the market after making the required profit (assuming the market moved in the right direction) it will re-enter the market again to repeat another trading cycle (hence the term PING-PONG).
(this can be either by selling first and then buying back, or buying first and then selling back depending on what your view on market trends is)

There are several configuration options to change the behavior of how CAT enters, monitors, and exits the market which is where most of the configurations come into play.
Once you get the feel of how CAT works and what options do what, then you can explore more complex configurations once you become more experienced with CAT and the currency pair/market you are trading.

As far as choosing which exchanges, im sure Sampey could suggest which APIs are most common but in order to start trading you will need to own some of each currency pair that you want to start trading so either select the exchange you already have been using before finding CAT (assuming the API exists) or setup a new exchange and transfer/buy the currency pairs that you want to trade.
Only other thing to consider first is to compare the fees, min order number, and the currency pairs available on the exchange, and what their trading volumes are.

After this, you will most likely be looking at individual currency pairs trying to decide whether to only trade one pair or split your money across multiple pairs and trade the entire market.
Once you make some money, you can buy another API and expand or experiment with other configurations to improve your returns.

Ill add this to the http://cryptowalk.com/ forum and expand further.

Regards Steve