计算机如何真正在计算机中请求数据？

I was wondering how exactly does a CPU request data in a computer. In a 32 Bits architecture, I thought that a computer would put a destination on the address bus and would receive 4 Bytes on the data bus. I recently read on the memory alignment in computer and it confused me. I read that the CPU has to read two times the memory to access a not multiple 4 address. Why is so? The address bus lets it access not multiple 4 address. I was wondering how exactly does a CPU request