Application uses Lightning Components that require My Domain. Before installing the package you need to check whether your org has My Domain. 

1. Open Setup
2. In Quick Find box enter “My Domain”
3. If you can see “Domain Deployed to Users” (see attachment), you can skip this step and start installation. In other case please create it first.

Creating My Domain:1. Enter your domain, press Check Availability and Register Domain 

2. Wait several minutes while Domain is being registered 

3. After Domain is complete, press Log In

4.Test all your processes and if everything is correct, press Deploy to Users.

Go to next step.