How to give 5% off for the second order

Does anyone know how to give 5% discount for each customer who place a second order? I can't figure out how…

Create a Promotions rule with value set to 5% based on user groups. You will then need to set customers to this particular user group to take advantage of this offer, not sure if you can have customers automatically added to a user group or not, but where there's a will, there's a way!

Just the second order? or the second, third, etc order?

You can create a discount CODE. Then put in the code in the invoice email

“5% off your next order” enter CODE “booya” at checkout