Most targeting is done using Categories. You can, however, target your subscribers at the time of sending based on the default fields for State, Country, and your custom date fields.

From time to time, you might decide you want to target your subscribers who have a certain attribute in common. To do this, you would find the subscribers with the same value in a default field  (like the same Company Name) or in a Custom Field (like subscribers who all indicate female as  their gender) and create a group, or Category, for these subscribers. Normally, you would export your list in order to find the subscribers who have the attribute in common. You would them re-import only the subscribers with this common attribute into the new category you've created.

Now that you have a category of the subscribers with a field or custom field attribute in common, you can easily target them during sending.