One of our MVP's (that knows a lot more about VSTS than i do) indicated finding Shelve/Unshelve can often be difficult to find and uses the command line to access this functionalityas a result . 

Having looked for it in the past i am not going to disagree and thought a couple of screen shots might be useful.

After the project is under TFS Source control you should be able to access the Shelve/Unshelve functionality one of the two ways.

1.  Bring up the Pending Changes Dialog one of two ways:

View > Other Windows > Pending Changes

Right Click a project in Solution Explorer > View Pending Changes

In this dialog both Shelve and Unshelve are on the toolbar (see image below)

2. Right click on a project or file in the solution explorer and choose Shelve/Unshelve.(see image)  NOTE: The context menu is highly dynamic based on what you right click and may not show Shelve - For instance right clicking on a directory doesn't offer Shelve as an option....