I believe you have seen a lot of different smart robot car, their basic functions are similar, basic movement, obstacle avoidance, line following, following and control by remote control, etc..
Here, we use the simplest structure to build a smart robot car, which can also achieve all the above functions. In addition you can control it with your cell phone, please refer to 8. IoT Car for the tutorial.
Here are some projects for the car, programmed in C with the Arduino IDE, if you are not particularly skilled with Arduino, you can refer to Get Started with Arduino.
The following projects are written in order of programming difficulty, it is recommended to read these books in order.
If you want to program a car with Scratch, please refer to: Play with Scratch.