Use this set of options to constrain your search on the type of card, and creature power/toughness.
All cards have both a Type and a Type mask. The card Type is very specific, whereas the mask is more general. For example, an enchant creature Type is an enchantment Type mask.
You can also search on creature power/toughness. This automatically reduces the search to creature type mask cards. Specify the constraining equality, and the value to compare against. Note that the special value applies to all values that contain a '*' or '+', or otherwise are not a simple integer.