Select another file you want to tag and open the context menu by clicking the right mouse button and select the ‘Tag with’ item. The last tag you used to tag is now the first item in the ‘Tag with’ list. This list can contain 10 items. In this case select the ‘My first Tag’ item.
The file is now tagged, the file icon will get a green tag overlay indicating that the file is tagged. The tags of a file are listed in the ‘Tags pane’.