On many datasets you can find a data dictionary--a description of fields in a dataset--as an attachment. You can find the data dictionary in two separate places.
Option A: On the dataset landing page
In the "About this Dataset" section, look for the attachments section. If it is not there, the dataset does not yet have a dictionary.
Option B: On the data view page
When browsing a dataset click on the About button along the top and scroll down to Attachments or click the Take me there! button at the top to end up on the dataset landing page.
Not all datasets may have data dictionaries attached. We are actively improving all existing datasets to include them. If one is missing, please contact support and let us know what dataset you need a data dictionary for and we'll get it posted as soon as possible. Going forward, all new datasets will require a data dictionary or equivalent documentation before being published to the portal.