Where is URL page with Clusters?

I have installed the shell and it works via CMD. the next chapter just opens with a webpage with Clusters /Security on it- have I missed a chapter or something? im confused

In Chapter 2: Creating an Atlas Sandbox Cluster, you will be taught on how to create your own cluster through ATLAS. There is a link provided in the lecture notes for your help.

Let me know if I can help.

Kanika