Multiplying fractions is easy: you multiply the top numbers and multiply the bottom numbers. For instance:
( 2/3 )( 4/15 ) = ( 2·4 ) / ( 3·15 ) = 8/45
When possible, you reduce. In the example above, however, nothing reduces, because 8 and 45 have no factors in common. If you're not sure whether anything can be cancelled off, you can always factor the numerator and denominator, and check for any shared factors.