In Greece, where I come from, herbs picked off the mountain are very commonly used as herbal tea. Simply pour boiling water over your chosen herb(s), let it steep, strain through a sieve (or use a loose leaf tea 'infuser' i.e. a sieve made to fit into a mug or tea pot). You can use fresh or dried herbs - which ones you like is all down to personal taste. I have used mint, chamomile and sage grown here, and when my folks visit I always ask them to bring me bunches of mountain herbs for tea.