After you open the Google spreadsheet, by default the file is named Untitled Spreadsheet so that you are not confused in finding your file later, you have to rename your Google spreadsheet file with the name of your work. Suppose you create a financial report in January 2017 with Google spreadsheet, then you can name the file with Financial Statements January 2017.
The result will look like the following picture:
If you have created a Google spreadsheet file, and you want to change the file name, you can go through the main Google Drive folder, find the file you want to rename the file, then right click and rename.
Write the name of the new file in the box provided, then click OK.
Similarly, how to name the file on the google spreadsheet, may be useful.