Reference

Keyboard shortcuts
Windows
Key
Action
Ctrl+F12
Default main activation key. Open options to add more or change it.
Main window
Key
Action
Enter
Execute the current suggestion (or the first one, if none are selected)
Escape
Close main window (or clear the input, if .ini file MainFormEscapeKeyAction is 1
Ctrl+n (1-9)
(most things) Execute the nth suggestion from the top.
(folders) Lists the folder's contents.
Ctrl+Enter
(folders) Opens the folder in Windows File Explorer.
(URL's) Opens the URL in a new browser window.
(everything else) Opens elevated (as Administrator).
Ctrl+Shift+Enter
(URL's) Opens the URL in a new, private/incognito window.
(everything else) Same as Enter.
Alt+n (1-9)
(files) Opens the nth suggestion's containing folder in Windows File Explorer.
(folders) Opens the nth suggestion in Windows File Explorer.
(everything else) Nothing (e.g. URL's).
Ctrl+Shift+n (1-9)
"Complete" the nth suggestion from the top (set the input text to it).
Ctrl+Shift+1
Toggle filter of only Start Menu suggestions.
Ctrl+Shift+2
Toggle filter of only file suggestions.
Ctrl+Shift+3
Toggle filter of only folder suggestions.
Ctrl+Shift+4
Toggle filter of only Control Panel suggestions.
Ctrl+Shift+5
Toggle filter of only URL's.
Ctrl+Shift+6
Toggle filter of only Google searches.
Ctrl+Shift+7
Toggle filter of only Wikipedia searches.
Ctrl+Backspace
Backspace over the previous word in the input.
Ctrl+Shift+Backspace
Backspace over the previous folder in the input.
Ctrl+Space
Cycle to the next most frequently used action cmd for the current input
Ctrl+Shift+C
Copy various texts from the current suggestion.
Ctrl+D
Delete/de-index/reset frequency of current suggestion.
Ctrl+Alt+E
Expand/contract paths
Ctrl+G
Activate the Google action cmd with the current input, to do Google searches
Ctrl+N
Creates a new file/folder using the current input. Creates intermediate folders if necessary.
Ctrl+O
Cycle to the next sort/order for the current suggestions
Ctrl+Q
Cancel/clear/quit the current input or current mode.
Ctrl+Alt+Q
Toggle input in double quotes.
Ctrl+Shift+S
Ensure current suggestion is saved/indexed.
Ctrl+comma
Switch to afterthought cmds for the current suggestion (lists the suggestion's context menu item).
For math expressions, toggle use of thousands separator.
Ctrl+Shift+comma
Switch to afterthought cmds for the current suggestion's parent folder, if there is one.
 

Glossary
Action cmd
A cmd that, when activated, puts the main window into a specific mode. Examples of built-in action cmds are:
g - Google search
gi - Goole Images search
maps - Google Maps search
w - Wikipedia search
i - IMDb search
Type an action cmd followed by 
Space to activate it. For instance, to start a Google search, type 
g, then 
Space.
Afterthought cmd
(aka afterthought)
A context menu item belonging to a cmd, once afterthoughts have been invoked for a given cmd. (The name came from the idea that you might think of an action for a cmd only after the cmd is suggested. So far, all afterthought cmds are simply context menu items for a cmd, but the name stuck.)
(Available via Ctrl+comma for the current cmd.)
Alias
A cmd that is a nickname for another "parent" cmd.
Aliases can have arguments, making their execution from the execution of their parent cmd. For instance, it is possible to alias 
Google Chrome, adding the argument, 
-incognito. Executing the new alias will open Chrome in Incognito mode.
Cmd
(aka command)
A cmd is executable item in the program. All suggestions in the main window are cmds.
Hitting Enter when there are suggestions always executes the first cmd, unless another cmd is selected, and then the selected cmd is executed.
In the main window, the distinction between cmds and suggestions is almost trivial, so this documentation will be guilty of using both terms interchangeably.
Complete a cmd
Set the current input text to a suggestion's "completion" text. For example, a suggestion might be a URL. Completing that URL sets the input text to that URL--specifically, the full URL, including the scheme at the beginning.
De-index
Remove a cmd from the FMS database.
Frequency
A cmd's frequency is roughly how often you have executed it, used to help rank frequently used suggestions more highly.
However, FMS remembers the frequency at the character offset level of your text input, so a cmd's frequency is not just one value. For instance, let's say you have a file named 
FMS.sln and you always type 
sln to call it up and execute it. Frequency will build up on the 
s in 
FMS.sln so that when new input similarly aligns, FMS will treat that cmd as frequently used.
Note that such alignment does not have to fall on a word boundary. For instance, if you tend to input 
care to call up and execute the URL 
https://www.marcon.ca/customercare, then frequency will build up on that alignment. In contrast, inputting 
cust one time will not rank the same URL highly, by design.
Single instance
When set to true for a cmd, FMS will attempt to switch to an already-running instance of that program, if one is already running.
(Available by right clicking the cmd > FMS > Properties > Single instance.)
Suggestion
An suggested cmd listed in the main window.
In the main window, the distinction between cmds and suggestions is almost trivial, so this documentation will be guilty of using both terms interchangeably.