To be divisible means that when you divide 468 by 3, the remainder is 0 (or the quotient is a whole number). 468/3 = 156, so yes, 468 is divisible by 3.
With 3 specifically, there's a trick you can use without actually dividing. If you add up the digits of any number, the number is divisible by 3 if the sum of the digits is divisible by 3. 4+6+8 = 18. It's a little easier to see that 18 is divisible by 3 because it's a smaller number than 468, so that's a helpful thing to know. 18/3 = 6, showing that 468 is also divisible by 3.