As soon as you open up your Mendeley web library, you'll notice the similarities with the desktop version. As mentioned previously in this guide, you can sync the two versions so that you always have access to your current sources, documents and notes, regardless of where you are.
When you login in to your Mendeley web account, look for the library tab as indicated in the image below. To understand the range of functions and customisation available, check out the Mendeley Web Library Guide.