To attach files from Google Drive, open the Card Details and click on the Attach a file button underneath the inscription Attachments. A request for permission will be showed to you. Accept it if you trust Kanbanchi to attach files to your cards. Choose a file you want to attach from the opened window of your Google Drive documents and then press the Select button.
If you want to attach a file from your computer, switch to the Upload tab in the same window. Click on the Select files from your computer button and then hit Upload.
Also, if the file you would like to upload from a computer is not very large, you can upload it to a particular card by using drag-n-drop. Just move a file from your desktop to the opened Card Details on a dashboard.
Notice: Files uploaded from your computer will be uploaded to your dashboard folder inside Kanbanchi folder of your Google Drive. These files will also have the same sharing settings as the entire dashboard, so your collaborators will have access to uploaded files.
There are additional actions you can perform with attached files. Open the Card Details and hover the mouse cursor on a file. You will see additional file options opposite to the file: