UPDATED April 2019 to replace quadrigacx with coinsquare in the example.
As I touched on in the last article, a trading pair is what you want to trade to and from. For example, at a traditional exchange at the airport, when I fly to Europe, I may ask them if they have the CAD/EURO trading pair. I want to buy (trade) Euros for Canadian dollars. A CAD/EURO trading pair will not only be different from USD/EURO because CAD and USD are different currencies from different countries, the pair exchange rate really matters. Some days it's better to buy bitcoin with CAD, sometimes it's better to buy with USD, or even a cryptocurrency like ETH(ereum).
Let's take a look at coinsquare as an example. The default page shows the high, low and current trading prices for BTC/CAD in terms of what someone is willing to pay in Canadian for a bitcoin, and on the other side of the order book tab, you can also see what people are willing to sell their bitcoin for Canadian dollars.
Most exchanges deal in several trading pairs, but to get started you need to find one that has your currency, for BTC. (CAD or USD, for example)
There's also usually a large arbitrage opportunity between exchanges. In the last month, it's not been unheard of to have BTC/USD on QuadrigaCX and BTC/USD on OKCoin have a price difference per bitcoin at over $1,000 USD!
OK, now that we get the value of trading pairs, let's jump over to everyone's favourite startpage, coinmarketcap.com which lists all of the popular cryptocurrencies by market capitalization. The first thing I recommend is looking at the coloumns that are available by default. I recommend you instead click on the number after Cryptocurrencies: in the top left. This will add all/views/all to the end of the URL, bookmark this page. I often get asked, where/how to do I buy $SOME_COIN, whichever coin they've just heard about, and the intent of this post is to resolve that. Simply find the coin on coinmarketcap.com, and then click on the name of that cryptocurrency. Once you're on the page for the cryptocurrency you're interested in, click on the Markets tab. Let's say I'm interested in buying Ethereum today, I click on Ethereum, then the markets tab, and I end up on the Ethereum markets tab. You can see, by default it lists all of the markets that have that currency as one side of the trading pair. Note that USD is different than USDT, avoid USDT as of reading this! So if I don't have any cryptocurrency yet, I'm going to be looking for ETH/USD or ETH/CAD pairs. If you're trying to buy a new cryptocurrency and it doesn't have a USD or CAD trading pair, it likely has at least a BTC trading pair, so go to the Bitcoin/#markets tab, find a BTC/CAD or BTC/USD pair, acquire BTC, and then go back to the Ethereum/#markets tab and find a ETH/BTC pairing exchange to trade there.
The last technical thing I'll leave you with on the markets tab for any currency is to click on the price header, so that it sorts by price instead of trading volume. If you do this on the Bitcoin/#markets tab, it's not unheard of to see +$5,000 gaps between trading pairs. Note, I don't usually trust any price that has less than 6 figures worth of trading volume (If I was an unscrupulous exchange I could say I bought a couple bitcoin for 20% more than elsewhere, so people to move to my exchange). Also note that today bitcoin has a long delay transfer time, so BCH/LTC/ETH are a lot more fun if you're experimenting with arbitrage of trading pairs.
If you are getting into trading, you should speak with your accountant, as in Canada it doesn't appear to clear yet how many trades constitutes you doing it professionally vs for fun, in which case it has different tax implications.