Hello Barbara,
There are two ways to do this. You can either use the export in the Integration Tools or List Builder. Each will give you different information.
For the export tool, you would use the Advanced Filter Options. For the export, setup a straight-forward export. Click Advanced Filter Options under the field list. Select Filter with script. You will then have to create a filter.
Here is a little explanation of the filter you need to use. The field where this string is stored is called Taglist so we need to search in this field. Tags are stored as a concatenated string of tags on the record. So we need to search for the certain tag within the string using the LIKE operator and % signs. It would be something like
WHERE Taglist Like '%tagname%'
Here is an example I used to filter contacts by the stoneage tag.
For the List Builder tool, fill your list with contacts. Go to Campaigns -> List Builder and click Fill list with Contacts... . In the menu, you have the option to insert contacts with only certain tags. See the Tags section at the bottom of the menu. Once the list is populated, you will get access to Step 2. There is an Export to Excel... at the bottom of the page. It will export all the information that is contained that is visible in Step 2 of the List Builder. The limitation here is that you are limited to information contained in the List Builder table and contacts.
I hope this helps,
Greg