The first time you save a Microsoft Word document, you need to give it a name and location. To do this, follow these steps:
From the FILE menu, select Save As.
Double-click Computer to save the file to your computer.
Selecting Save As opens up a dialog box in which you can see:
The document location, or where on your computer Word will save your document. You can select a new location by clicking on the arrows.
The file name. Note that this is highlighted as Microsoft Word expects you to choose your own name for the document. Simply begin typing to do so.
The file type. Note that this defaults to ".docx", which is the default file type for Microsoft Word 2013 documents. When final, you can choose to save your document as another type, such as a pdf, simply by choosing "PDF (*.pdf)" here.
After you have entered these fields, simply click Save to save the document.