It's not very obvious how to organize your files in Google Drive so that you can place a document under multiple folders. Here's how - follow these simple steps:
To organize files under multiple folders in Google Drive, you just need to hold your CTRL key and select the folders.
1. Select the file. If you want to choose more than one file, check each of the checkboxes on the leftside of the file.
2. Under the More option located underneath the search button, click on "Organize". This is the icon that look like a Folder. This will open a popup dialog box. OR simply click on the Folder icon.
3. In the Organize popup, press the Control Key on your keyboard and select the folders in which you want to move the file(s) to. You can select any number of folders by pressing the CTRL key. You will see a 'check mark' for each of the selected folders.
4. Click the blue Move button. Once you do this, your file(s) will move from your main My Drive section into the folder(s) you selected. This action does not create multiple copies of your file. The file remains a single version, and if you edit it in one place under a certain folder, that edit will show up on the file located in a different folder.