I need an app or a website that can provide me with tools I can use to create a graphical framework of a mobile app for my assignment presentation. I am to provide a business problem and tell why it is necessary to invest your time and resources to provide solutions to the problem then propose a mobile application solution to the problem. I don't know graphic designing and I am just beginning the course. I only need a site I can use to create a mockup or screenshots of how my application user interface will look like
I try mockup.com, canvas, photoshop but I am not familiar.