"reducing a fraction to its simplest form" means "cancel out any common factors of the numbers on the top and the bottom".

For example, has a common factor of as .

In the example given, I presume you're supposed to use the Eclidean algorithm to get the highest common factor of the two numbers given. You can then cancel out (i.e. divide both top and bottom) by that factor.

From the form of the second part of the question, I assume you're studying basic number theory, in which case you ought to have covered these aspects in your course work.