Answer:

Arithmetic modulo 5 can be thought of as arithmetic on a clock with the numbers 0, 1, 2, 3, 4.

For example, to find 3 + 4, start at 3 and go round 4 spaces, arriving at 2. This can be written 3 + 4 = 2 (mod 5)
Similarly, 2 x 3 (2 lots of 3) can be interpreted as 3 + 3, which is 1 in clock arithmetic: 2 x 3 = 1 (mod 5).