I'm new to Appian BPM World, I was wondering how the end user access the application which is build on the Appian BPMM tool

You can access Appian applications as standard Web-based applications (using a browser) or via the Appian App (when using on a mobile device).

thank you stewart for quick response, i mean the end user need to access a URL and credentials, if yes what type of authentication that would be ??

Appian provides its own basic authentication (userId, password) or you can implement a SAML-based SSO authentication mechanism if you have an IDP you want to leverage.

thank you, one more question, if you don't mind, if some one asks, what are the challenges you faced in Appian development, i know it's broad question, can you please share your experience.

Yes, too broad to do it justice. And the answers might be different depending on the individual's experience, both Appian and broader development experience.

Can you share anyone of yours, so that it gives me idea to answer to that question, i have interview on Monday,it would be of great help.