2SC1815(Y) and 2SA1015(Y) are made by TOSHIBA, a renowned transistor family as multipurpose amplifiers among hobbyists. Ranging from middle wave detection to low power amplification. Hobbyists like these as parts of superheterodyne receivers. They have already deprecated and not been lined up as new products, but you may find these stocks on shops. Equivalent to NPN 2N3904 and PNP 2N3906 of Fairchild (ON Semiconductor).
Flip-flop is a digital circuit to store a bit, which is used as registers in CPU. But as you know, state-of-the-art registers are so tiny because of using MOS (Metal Oxide Semiconductor), Multi-dimensional Architecture, and high power microscopes. Besides, this schematic uses bipolar transistors, and much bigger than real flip-flops in the CPU of your computer. But You can find and learn its unique feedback process for flip-flopping. Flip-flop has variations. On this schematic, I introduce D type which inputs are Clock and Data, similar to signals in computers. Check the Wikipedia Page for D Flip-Flop.