is it possible to create web application using ionic or is it only for mobile ? what is the difference between Angular and Ionic
You can definitely do it. However, it's probably not advisable. Ionic just provides a bunch of directives for you to use. You can use that in conjunction with something like Cordova/Phonegap to package that up for a mobile release. Otherwise, you could just take the web parts of the project (i.e. all your html/js/css/assets) and point a web server to them and presto - you can access your ionic page with a browser.
You probably don't want to do this for a few reasons.
My suggestion here is to just use plain Angular or another framework such as React/Vue.
To answer the last part of your question: Angular is the framework that Ionic provides bindings (and some assets such as icons) for. Those bindings happen to be optimised/targetted towards mobile devices.
Hopefully that helps out a bit.