Make sure you select the “Installable WordPress file only” option. If you select “All files & documentation”, you will not be able to install this zip as is. Instead unzip the file and then locate the installable theme file within it. Luckily most developers clearly label their files, so it should be pretty easy to find.
Also you can unzip your purchased download (All files & documentation) and check the theme documentation hopefully you will get necessary support in documentation how to install and all necessary help.
If you have still problem with the theme then The best way to get the support is Contact your purchased Theme Author. Contact Author because Item Author are best expert about their Item functionality.
I think yur theme bundle plugins included contact form plugin. you have to use that plugin to create. otherwise have to install contact form plugin (as like contact form 7) and create your form. when you will create form you will get shortcode (in contact form 7) and you can copy and paste the shortcode where you want the form need display.
How to contact an author to get support or for any technical query: