Hi, welcome!
The swap partition (known as a paging file in Windows) is where physical memory (RAM) is temporarily stored to disk., usually when the system is low on RAM. System performance temporarily drops when the system is “swapping”, and the system would lock up if it’s out of memory with no swap.
For the Raspberry Pi, by default, no swap is created as this would wear out the SD card and degrade performance even further. It’s not essential to have swap, but desired for a standard computer.