Define/Explain
Can I use it is a tool to let you know if and how well different browser will support web technologies. For example if I wanted to use the CSS flexbox layout I can know for certainty if it will display and act accordingly whether the end user is using Safari or if they are opening the web page in Internet Explorer.
Specific Uses of resources information
The specific use is as mentioned above. If I want to know if a specific style will work on a specific browser I can reference this page and it will give me the foresight if it will work if the end user is using a specific browser. If we continue to use Flexbox as our example, it will not display correctly on versions 6-9 and only partially on 10 and 11. Another use is if there are known issues, canIuse will give you a detailed list of its known issues. Ex. "IE10 and IE11 on Windows 7 have a bug where translate transform values are always interpreted as pixels when used in animations test case". There are links for additional resources to continue reading on the subject, and a place to provide feedback.
Properties
Learn more about animations
Learn more about anchors
Summary
CanIuse is a great reference to make sure your content/creation will work well for your audience. It allows you to know what to expect when using elements/attributes/properties and which browers and versions are equipped to recognize them.