So if you took one of these F1 auto and used STS to create pollen, then used that pollen on another on one of these F1 autos, then you will have an F2 auto. The F stands for Filial or family.
The S1 would be if you took that pollen and pollinated the same plant, that would be an S1. The S indicates that the plant was Selfed, that is the same plant was both mother and “father”.