For now click the create new app tab at the top right corner.An ajax alert like window opens,
Provide an app name,and you have to then provide a unique name in name space which is then used to identify your app.Also in case you do not have hosting facilities,you can sign up for the free hosting at heroku.
Pass the subsequent security check to prove your not a bot.
Then if you encounter “You’ve been blocked from creating apps because we haven’t been able to verify your account” , this means you have to verify yourself by going here the verification requires a government issued id with name, date of birth and photo .Once verified you will be good to start your apps.
Upon success you will be given app id and secret key.
Now in a text editor compose your app code,Then go to app on facebook tab,in the canvas url provide your code file name which you have created in the default localhost folder,The secure canvas requires you to just replace http with https.
Save the changes.
Then visit https://apps.facebook.com/your-app-namespace. viola its your app!!
To develop the app in localhost check out this