Memory cells (addresses) read into a cache
Cache lines are aligned.  That means that the bottom-most bits of the start address of the cache line are always 0s.

If you have 8-byte cache lines they will always be read in address ranges $[8i, 8(i+1) - 1]$.  For example, if you read address 117 (decimal) = 1110101 (binary) then the 8 byte cache block that gets read in is the set of bytes in the range 112 (decimal) = 1110000 (binary) through 119 (decimal) = 1110111 (binary).