A bit is always implemented as something electrical. About 100 bytes. About one million bytes. About one billion bytes. Each byte of main memory has a unique address.
Main memory consists of a very long list of bytes.
Each memory location can store any number of bits. Memory addresses are positive integers starting at zero. It can write 8 bits to a byte in memory, and it can read 8 bits from a byte in memory. It can erase a byte in main memory, and it can read a byte of main memory. It can add the value from main memory to a sum, and it can print the value on the monitor.