How to get 2D map using Stereoscopic camer (RGB+D), IMU and GPS?

Question

I am starting with slam using imu, stereo camera (that gives RGB + depth info) camera and gps mounted on my robot. I wish to create a 2D map for it like this:

But with landmarks, so that I can stop the robot near those landmarks.

I am unable to find a good way to structure this.

How should I start with this. What all steps are needed to implement this ?

Thanks and Regards.