On the Advanced Search page there is a link in the top right, 'Use the search builder' which changes the search form to the search builder layout.
The search builder is a sophisticated searching tool that allows you to build up a more targeted search query by setting up one or more search 'clauses'.
In this context a search clause is a specific condition (such as Orientation of an image is equal to Landscape) that must be met for an asset to be returned in the search results.
For example, specifying the above clause alone would return all assets in the system which are images (only images have an orientation attribute) with a landscape orientation.
You can be more specific in your search by adding additional clauses:
Now the search will return all landscape images in the system whose titles contain the string 'mountains'. The relationship between the 2 separate clauses is by default set to AND, which means both clauses have to be met by the asset for it to be returned as a search result. You can change this to an OR relationship using the dropdown box between the clauses. In the case of an OR relationship the search actually becomes more general as it will return any assets that: are landscape images; or, have the string 'mountains' in the title.