You can use labels for your tasks to filter it down when you need to access a certain task or tasks from a certain group. Labels for tasks and files work in similar ways.
You can add the label by clicking on the task and it will bring the side bar menu, you will see a sign of a tag on the top of the side bar menu. When you click on that, it will bring up a text box which will allow you to use an already existing label for the task, or add a new one.
To find the labels that you would like to filter down, press the funnel at the top of the task page and it will bring another side menu with all the labels there are and you can click on the label you would like it filtered down to.
You can edit or delete the label by clicking on the pencil that will be next to the label and it will bring up the box shown in the image below.
And you can change the name or delete it from Glasscubes totally by clicking on the bin in the bottom left corner then pressing ''Save''.
To view how to use labels on files, see here