Raspberry Pi SLAM - Where to begin

I'm trying to build a navigation system for a robot that uses a rasbperry Pi zero board and an arduino ultrasonic sensor. I've seen bits an pieces of the technology in a range of articles and videos, however I haven't really found a guide of where to begin to implement this with Simulink.

I'd like to run the algorithm solely on the raspberry pi (without connecting to an external device for data processing and such).

If someone could help me with this, it'd be an immense help as I'm a bit overwhelmed as to where I should begin with this.

Thanks,

:)