Taxonomy and Views - Creating a view based off of user selection
There are a few ways to accomplish this; i'll offer up my easy answer.

You can show all of the nodes associated with a taxonomy tag by adding the "Taxonomy: Term" filter (select the taxonomy term ID filter). Select your relevant vocabulary, and then select 'dropdown' for your Selection Type.

Click 'Expose' to show a dropdown box to your users. When a user selects a tag from your dropdown, your results will be filtered according on the Operator you have chosen.