When you first get to the www.flourishkh.com site it will look like the following image.

The Login link is in the upper right hand corner of the site, slightly below the three links for K-12 Programs, Free Resources, and How To. 
When you click on the Login link, a dialog box will appear in the middle of the screen that will ask for your username, password, and PIN. If you don't remember your password use the 'Forgot your password?' link in the dialog box. 

If you need help with your username or PIN you can always contact the technical support desk in the following ways:
Technical Support
Live Chats are available at https://help.kendallhunt.com/k12-customer-support by clicking the "Start a Chat" button and choosing "Technical Support".
Live Chat Hours:
Monday – Friday: 8am – 10pm CST
Saturday: 9am – 9pm CST
Sunday: 9am – 10pm CST
Support Requests through email can be submitted at techsupport@kendallhunt.com.