Urgen help needed on page theme

Hi guys,
I have just hit a brick wall on my wordpress site. I am creating a directory website where businesses can advertise themselves and the problem i have is that i have the theme twentyeleven installed i think which is the stock template theme for wordpress. Now i would like to edit what is in each of its page, for e.g. home, about, contact us…. How do i change the layout of each page and delete some of the existing categories. Also how do i add content such as about us on a page.

Help would greatly be appreciated. Also is there any drag and drop wysiwyg plugin that is free that i can use to do this?

Thank You