This article explains how a user can search for files in a SharePoint site.
Searching in SharePoint
One of the nice features in SharePoint is its search bar. All you have to do is type in a key word, like an author, document type, or describing word, and SharePoint will print a list of all relating files.
It is recommended to use single words when searching, but if you need multiple key words, like a document type and an author, use the AND or OR operators in between your key words.
In the image below, I selected a document library that I wanted to perform a search in, and typed the key word 'Word' to find all of the .docx type documents.