If you already installed the wordpress, you must check your wp installation. Choose random prefix, for example [random_demo] for your tables to avoid over-writing any existing database tables and also for the security purpose. Also while creating Username and Password, avoid the username and password as admin and admin. Set the username and password randomly. If you are freshly installing the wordpress follow the above steps.
When you download the theme from Themeforest, you will get an archive file in .zip extension. You need to unzip that archive file. The mist.zip file is the Installable WordPress Theme and what you need to use to get the theme installed. Please see the following steps that how to install Mist.
If you are going to install the theme using FTP, you will need an FTP Client, such as FileZilla. After unzip the mist.zip file, you should see Mist Folder and follow the steps below to install the theme via FTP:
Mist includes 4 plugins that will need to be installed and activated: Revolution Slider, Visual Composer, Zozothemes Core, Ultimate VC addons. Only the Zozothemes Core plugin is required one to work for our theme features like shortcodes and shortcode generators. Revolution Slider is recommended plugins. Visual Composer and Zozothemes Core are required plugins. When you install Mist, you will get a notification message in your WordPress admin telling you of the required and recommended plugins.