Formal and plural commands use the -ga form, exactly as the mood tense rule predicts.
Salga · Salgan · No salgan · Póngalo aquí · No lo ponga aquí · Téngalo
And the positive ones still put the little word on the end: póngalo, téngalo.
Regular verbs drop the s from the informal you form. These verbs have their own shortcut: drop the -go entirely.
tengo → ten · vengo → ven · salgo → sal · digo → di
Tenlo · Ven · Sal · Dime
Both are what you hear when people answer the phone, in Spain and elsewhere, which makes the pair easy to remember.
The venga you hear in Spain meaning come on is not really functioning as a formal command any more: it has become a fixed expression.
Worth holding the two side by side, since they differ.
comes → come · encuentras → encuéntralo
tengo → ten · digo → di
Combining a command with a future cuando puts two different mechanisms in one short sentence.
Dime cuando vengas · Dígame cuando lo haga
The command uses its shortcut or its -ga form, and cuando takes the mood tense because it refers to the future.
Everything in this track follows from knowing a verb is a -go verb.