Every forex chart will be labeled with a currency pair: EUR/USD, USD/GBP, etc. Remember, all forex trading deals with different countries' currency in relation to each other. The EUR/USD chart, for example, tells you how the euro and the U.S. dollar compare.
Along the bottom of the chart is the timeline -- 15 minutes, an hour, a day, a week, or some other period. Going up the right-hand side are incremental amounts. For the EUR/USD chart, the amounts might be 1.2531 at the bottom, going up to 1.2561 at the top. And of course the middle of the chart shows what position the EUR/USD pair held at what time.
The forex chart is useful because it shows in graphic terms how a currency pair is doing. You can see at a glance whether a currency is getting stronger or weaker, and you can act accordingly. Choosing the time frame helps you see very minor trends (in a 15-minute period, say) or more long-term ones (over the course of several days, perhaps).
You can find forex charts all over the Internet, on Web sites for forex brokers, tutors, and on other forex-related sites. Those are fine for glancing at trends now and then. But to be a serious trader, you need to have access to charts much more readily, without having to go to a Web site. That's why trading software gives you forex charts, too (you need to have broadband Internet so you can be "always connected"). Obviously, if you're going to be trading, you need to have convenient access to the very latest charts.
With dozens of world currencies, there are far too many possible currency pairs for anyone to keep track of mentally. Forex charts show at a glance what any currency pair is up to, and good software allows you to save multiple charts as "favorites." Naturally you'll want to keep an eye on the charts representing investments you've already made, and it's smart to have a few additional ones saved, too, so you can watch for trends in currencies you haven't traded yet. You never know when a lucrative new opportunity is going to be revealed.