Each file stored in Google Drive should have a unique name to identify it. All files, including Google Docs, Sheet and Slides, can be named after they have been created - if you need to rename an existing document, this can be done via the docs list.
To rename a document in the docs library:
Select the document you wish to rename by clicking once on the document
Click on the More Actions button along the top of the document list
Choose Rename
Type a new name for the document, then click on OK
You can also rename a document by right-clicking over the document and choosing the Rename option: