Dimensions that are not in use are displayed as blue buttons within the illustration page.  When you first begin, most of the dimensions are blue, because you have not told Cytobank which ones are included in the experiment.  

To activate a new dimension, click the name of that dimension in the illustration (e.g. click "Conditions").  This will turn the button orange and open a dimension box that is empty.  Within the dimension box will be a link saying, "Click here to edit..." -- click this link.

When you click a link to create/edit a dimension, you are taken to a page that lets you edit that dimension.  In the upper left of this page is a text area where you can enter a comma-separated list of things included in that dimension.  For example, if your experiment included two Conditions, Unstimulated cells and cells stimulated by the cytokine IL-4, you could enter "Unstimulated, IL-4" and click "Add".  

Once you enter a comma-separated list of dimensions, Cytobank searches within your files for that text.  If a file matches, it it tagged.  In the example of "Unstimulated, IL-4" you would see two columns appear, one for each dimension member of "Unstimulated" and "IL-4" and within each would be a list of the matching files.  You will also see a list of the untagged files.

You may drag and drop files between the tags to re-assign them.

Once you are done, click "Return to Illustration" in the upper left.