Displaying part of a random webpage from a website

To preface, I am a beginner java learner trying to figure out what I need to learn / master before I can tackle this problem. So I am looking for broad stroke / process needed to achieve this.

I am trying to make a program that displays a random page from a medical image atlas website, while hiding most elements from the page but the picture. Then with a click of a button, the comments/description is revealed. This program would be great for studying/reviewing spot diagnosis or teaching.

The website url format is /image.asp?n=X&Case=Y
where X = picture # from specific disease entity and Y = Disease entity. The X can be up to 50, and Y up to 750 (broadly grouped by organ system)

Ideally the program would generate a link with random X and random Y within that range, test to see if the webpage exist. If not, repeat; if it does then it gets fed into the program that hides certain elements from the webpage. Clicking a button would reveal the element that contains comment/description of the image.

What's the best way to accomplish this using java? What do I need to learn to attempt this?

Thanks