Hi, a bit late here but here goes, it is a herb and it has a similar flavour to Cilantro but with a wee Basily taste too and depending on which colour you have grown it may seem a bit lemony. Use it as you would any other herb, it is just a matter of taste. Don't over do it as it can be a tad bitter especially of the leaves are a bit older.
If you want specific recipes I am certain you would find them if you googled "how to use Shiso" or something like that.
I used to grow all three colours when I made a lot of sushi which I don't now but I only ever used the red and the green,( the red I used in a Japanese pickle recipe) the green generally and for the sushi, it goes well with chicken and pork, white meats rather than red and not in say spaghetti sauce by the way but there will be lots of recipes out there. The variegated I grew cos it was pretty.
If you don't find any recipes let me know and I will get a few from my books for you.
XX Jeannine