Morningstar is just a research firm. They are mostly known for providing analysis and ratings of individual stocks and mutual funds. It's basically a resource to help you make investment decisions. If you want to purchase shares of a commodity-based ETF, you can do that through your regular brokerage account. ETFs have ticker symbols just like stocks, and you buy or sell them the same way you would buy or sell an individual stock.
You can actually get lots of info with the free membership - you just have to register. One thing about them I don't like though is that they seem to have certain technical glitches that occasionally lead to login issues, and they've never responded to those issues I've had - I've found that I've had to re-register there several times over the years. Of course it may be that the free membership expires after so long or whatever.
