The article explores the use of information as a means of changing activity. Information is conceptualized as a type of message that triggers a change in activity. It is argued that there are two main ways to induce change in activity. One way is through descriptions of reactions on message/data received. But in case such descriptions are absent, the more complicated way is through solving practical problems of such descriptions’ construction. These problems manifest as questions about descriptions needed—without immediate answers. Once the answer is found and the problem is solved, the agent’s (person, actor) activity can be modified based on the solution obtained in the form of activity description. It is argued that problem-solving is inherently an informational activity, aimed at altering the agent’s behavior in accordance with the received message(s). The author contends that practical problem-solving is a primary means of information application and a defining characteristic of informational activities. The core concepts and methods of this approach are examined. A transformational perspective on problem formulation and resolution is proposed. The conceptual results presented were tested for the classification of practical problems and the formulation of some practical problems as mathematical ones. This paper can be used for the application of the conceptual means presented to formalize problem-solving, such as problem of information technology use efficiency estimation and new information technologies application, such as suggested digital twin of activity technology.