The fact you purchased a domain is irrelevant.
You can select widgets of your own choice and override the default theme display here > Appearance > Widgets.
select the ones you want one at a time, click to open , confure where required, click "save", click "close".
The front page of the blog by default will display your posts (not pages) in reverse chronological order, with the most recently published post on top. If you do not want all the posts to show on the front page, then you can create a static front page “Welcome“ for your site and a “Blog” page for posts. http://en.support.wordpress.com/pages/front-page/
You could read the theme description and follow the instructions provided there. http://theme.wordpress.com/themes/oxygen/
There is no "slideshow". There is a featured post slider.
Showcase page template
When you first activate Oxygen, you’ll see your posts in a traditional blog format but if you’d like to showcase your content in an online magazine-like fashion, then you can use the Showcase Page template.
The Showcase Page template offers a featured slider for Sticky Posts. To use the template, create or edit a page, and assign it to the Showcase Page template from the Page Attributes module. If you’d like use the Showcase Page template on your front page, go to Settings → Reading and set the Front page option to Static Page. Select the page you just assigned the Showcase Page template to as your front page and then choose another page to serve as your blog page.
Oxygen featured post slider:
Sticky post thumbnails are 750 pixels wide in the featured slider
Regular post thumbnails are 450 pixels wide
template > http://en.support.wordpress.com/pages/page-attributes/#template
setting a Featured Image > http://en.support.wordpress.com/featured-images/#setting-a-featured-image
designating a sticky post > http://en.support.wordpress.com/posts/post-visibility/#sticky-posts