The following figure is just a simple structure of LUT (look-up table) in the above figure. You just need to know that LUT is based on ram structure.

The above picture shows the internal composition of the basic unit CLB of fpga. If you know the composition of CLB, you can have a general understanding of fpga. My brother has been studying FPGA for less than two years, but in the process of writing code, it is nothing more than clock, carry and cache. Therefore, for general applications, CLB is basically sufficient. For those internal integrated blank ram, shift register, internal fifo and buffer, it is just for convenience. To understand these structures,