There are a number of ways to randomize certain aspects of commands, E.G.:
Doing so within the "Say Something with Text-To-Speech" action is detailed in the official documentation (press F1 while VoiceAttack has focus to open VoiceAttackHelp.pdf in your default PDF viewer, which contains information on VoiceAttack's features), so I'll assume you're aware of that already.
The "{TXTRANDOM:}" token can be used with the Quick Input action, if you're looking to type (partially) randomized text
And, of course, the "Play a Random Sound" action is intended to do exactly what its name suggests.
If you want to randomize which action, or set of actions, is executed, the simplest way may be to use the "A random value" option of the "Set an Integer Value" action, combined with a set of conditions.
E.G.
Set integer [~randomValue] value as random from 1 to 3
Begin Integer Compare : [~randomValue] Equals 1
Press A key and hold for 0.01 seconds and release
Else If Integer Compare : [~randomValue] Equals 2
Press B key and hold for 0.01 seconds and release
Else
Press C key and hold for 0.01 seconds and release
End Condition
These topics may also be of use, in addition to the official documentation, if you'd like to understand the features utilized in the example:
Control flow (If, Else, ElseIf, Loop, Jump) basicsVariables and tokens summed up