Existing task models have often been used in the context of graphic systems. In this paper, we propose to use the task model at runtime to monitor user actions, to verify that he/she has not made a mistake when performing his/her actions and to give him/her help when necessary. In particular, we present, as a first contribution, a task model specific to interactions in ambient environments. This model enables to assign dynamic characteristics to each task thereby allowing to a supervision system to assign states to tasks at runtime based on the information exchanged with the environment (start of a task, end of a task, preconditions states...). Our second contribution is a monitoring and support system that exploits our task model. More precisely we specify the intervention strategy of our system in order to guide the user. We present then an illustration of our system through the execution of a scenario on our simulator. This simulation shows how the interactions with the task model at runtime allow us to produce a dynamic system that takes into consideration the context and provides assistance to the users while carrying out their daily tasks. Finally, we end with a conclusion and perspectives of our approach.