The mouse is the primary controller for Warcraft: Orcs & Humans: normally selects menu options, units, structures and their command icons when highlighted by the cursor, while normally deselects or cancels.
However, it can still be (extremely) useful to learn keyboard hotkeys, particularly for commanding Units and Structures, although these hotkeys may vary depending on context: for example, after selecting a unit and pressing A you can normally select a target for that unit to attack, but doing so with a Peasant or Peon commands them to build an advanced structure (when possible).
Hotkeys are normally highlighted in text labels, which serves as a quick reminder should you forget them.
F10 after starting or loading a game pauses it and opens this menu.
Key
Function
S
Save Game
1 - 7
Save Game 1-7
O
Options
G
Game Speed
M
Music Vol
S
SFX Vol
U
Mouse Scroll
K
Key Scroll
Key
Function
L
Load Game
1 - 7
Load Game 1-7
R
Restart scenario
C
Continue
Q
Quit
D
DOS
M
Menu
C
Cancel
After selecting a Save Game, you can type in an 18 character description before pressing Enter (don't, and it's labeled NO NAME): if you change your mind after selection, then press Esc, not C.