beginner asp.net website access

this is an absolute beginners question.

Our local library has a web-site and I like to write a custom application to see the books I lend out. In a second step I like to have a button in my app to lend them out for an additional two weeks or so.

How can I do this? What should I read in advance? Which tools will I need?

If there are any special tools takle into account that I am mac bound.

It seems to me that the site is build using ASP, but I am not sure how to tell this for sure...

So many questions Thanks for your answers / hints