A more thorough explanation:

Definition: Forthwith means immediately; promptly; without delay; within a reasonable amount of time under the circumstances.

• The manager requested that the report be completed forthwith.
• The company promised to deliver the product forthwith after receiving payment.
• When the fire alarm went off, everyone evacuated the building forthwith.

These examples illustrate how forthwith is used to indicate that something needs to be done immediately or without delay. In the first example, the manager is requesting that the report be completed promptly. In the second example, the company is promising to deliver the product within a reasonable amount of time after receiving payment. In the third example, everyone evacuated the building immediately after the fire alarm went off.