the robot does not know its position when it is activated what is the solution with ros so that it knows its place and I work with lidar

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It sounds like you're new to ROS, so I'd recommend checking out all the available tutorials found here.

This tutorial covers tf, which is how your robot will keep track of different coordinate frames (the relative position of sensors, wheels, and the environment).

There's several solutions to localization (where the robot knows its own position), but a very common one is robot_localization. It is documented on this wiki.

Localization is usually done through fusing multiple sensor types (imu, encoders, gps). But from your question, it sounds like you want to achieve slam through using a lidar only, so you would be interested in hector_slam documented here.

PS you tagged your question ROS1 so I'm linking you the tutorials for that version. If you're new to ROS, I'd recommend just starting with ROS2, which has tutorials documented here.