If you are new in angular and your facing below issue during the creation of project then your on right place.  

ng is not recognized as an internal or external command 

Let's follow my instruction and get out from issue.

Step 1) Create one folder anywhere on your system eg :- my folder (C:\~\Desktop\AngularApps).

Step 2) open  folder in CMD as below screen

Step 3) Run Command in cmd(npm install -g @angular/cli)

Now Create new project using => ng new [Your project name] e.g :- ng new myFirstProject.

Thank you!