The first time you save a document, the word application will default to the save as option save the document automatically create a new folder for you to save your work save the document as "document 1"

default to the Save As option

The first time you save a document, the Word application will default to the Save As option. 

This occurs to give the user a chance to save the document with a name that pertains to the content of the document. This also ensures that the document is easier locate for the user on subsequent occasions.