Visual Studio can help you find the answer to your question in a couple of different ways.
Type Ctrl + Q to access Quick Launch, and then enter "collap". Quick Launch will display something like:†
Menus (1)
Edit -> Outlining -> Collapse to Definitions (Ctrl+M, Ctrl+O)
NuGet Packages (1)
Search Online for NuGet Packages matching 'collap'
From there, enter "outlining" to find other menu entries related to outlining:
Menus (5)
Edit -> Outlining -> Toggle Outlining Expansion (Ctrl+M, Ctrl+M)
Edit -> Outlining -> Toggle All Outlining (Ctrl+M, Ctrl+L)
Edit -> Outlining -> Stop Outlining (Ctrl+M, Ctrl+P)
Edit -> Outlining -> Stop Hiding Current (Ctrl+M, Ctrl+U)
Edit -> Outlining -> Collapse to Definitions (Ctrl+M, Ctrl+O)
Options (4)
Text Editor -> Basic -> VB Specific (Change outline mode, Automatic inser...
...
However, note that Quick Launch will show you only those commands that are available as Visual Studio menu entries. To find other keyboard-related commands related to collapsing sections of code, in the Visual Studio menu bar click:
Tools -> Options -> Environment -> Keyboard
This will display the keyboard section in the Options dialog box. In the "Show commands containing" text box, enter "edit.collap". Visual Studio will display a list that is something like:
Edit.CollapseAllincurrentblock
Edit.CollapseAllOutlining Ctrl+M, Ctrl+A (Text Editor)
Edit.CollapseBlockcurrentblock
Edit.CollapseCurrentRegion Ctrl+M, Ctrl+S (Text Editor)
Edit.CollapseTag Ctrl+M, Ctrl+T (Text Editor)
Edit.CollapsetoDefinitions Ctrl+M, Ctrl+O (Text Editor)
You'll need to click each command to see its associated keyboard shortcut.
† My examples taken from Visual Studio 2013.