The Boolean NOT operation is a negation of its input.
That is, the output of a NOT gate is NOT its input.
Look at this Truth Table
In schematic logic diagrams this is represented as a small circle on an input, or output, or as a buffer (triangle) plus the small circle. It is also commonly represented in notation as an overscore on the negated terms.
Time to build your own robot! Using a Raspberry Pi with parts and some time, you can use my book to learn how to make and program a robot with automatic behaviours.