If an article does not have a "Free PMC Article" link option in your search results list, don't abandon it just yet! Click on the article to open its detailed information page. On the right-hand side you'll find a familiar button: UI Link!
The other full-text options may try to charge you money. Don't ever pay for an article! If there are are no University of Iowa databases that have access to the article, select "Request this article by Interlibrary Loan/Document Delivery." It may take a day or two for you to get the article, but it will be free!
Article types in PubMed are going to be different than what you're used to seeing in more general databases such as Academic Search Elite and ProQuest. They will be much more specific to the kinds of research in the PubMed database - biology, chemistry, and health sciences researchers write papers and reports that are quite different from other fields, particularly humanities fields. After you have entered a search term and are on the search results page, the top left corner is where you will find the "Article types" filtering option. "Clinical Trial" and "Review" are the two options you will always see when you first search PubMed, but clicking on "Customize..." will open a smaller window that lets you choose from a much larger list of article types. Once you select some more article types and hit the blue "Show" button at the bottom of the window, those types will appear in the list you see on your results page. Now you can click any of those types to narrow down your search!
PubMed offers some help right from its home page - choose any of these links in the left column below the page header to learn more about using the database. Just need to know where to get started? Choose the "Quick Start Guide." Want to read or watch some tutorials? Choose "PubMed Tutorials" - this link includes both text/still image tutorials, as well as videos. "PubMed FAQs" is another good place to look if you are having trouble with your searches.