Tulsi (or tulasi or holy basil) is a revered Indian herb and is used medicinally across Asia. It is simply a basil and is in the Lamiaceae family as is mint and balm.
There are many tulsi variants and each brings a beautiful aromatic flavour. Tulsi can be quite floral, pungent and aromatic, or lemony. The flavour is hard to describe as it is very uniquely tulsi. I find it uplifting and great for a morning drink. Research shows it can support mental clarity, and a wonderful herbalist once told me to gargle with it if you have a cold as it has anti-viral properties.
In Ayurveda and traditional medicines, all parts of the plant are used. In the tea we use the leaves which are dried and chopped to just the right size. You can grow tulsi on your windowsill but like basil is a little too delicate for our English weather.
Have a look at the tea.