You can create a simple "Hello World" application using Interplay.

Start with an HTTP node "GET" request and name the URL. Click on done and click deploy.

Also, add the HTTP Response node along with a NodeJS Function node. Connect all the nodes.

Click on the NodeJS Function node. Add 

 msg.payload = "Hello World"

Click on done and click on deploy.

To test if the Hello world application worked, go on the browser and type 

 https://(your_instance_name).interplay.iterate.ai/(Get request name)

The same can be achieved by using Express node instead of HTTP wherein you can control your functions and logics to achieve the desired results.