If the WordPress account is from WordPress.com then this will no work with Themeforest items.
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you need to have your own hosting and domain
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download WordPress from www.wordpress.org OR depending on your hosting provider you may be able to install it directly from the admin
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once WordPress is installed on your domain/hosting then you can upload the theme
There’s no need for JetPack and bear in mind that the theme may not include the images and will not look like the demo until you have imported dummy content/created content and configured he site setup e.g. applied navigation, front page, etc.
If none of this makes any sense then you may find i easier to get a freelancer to help from www.studio.envato.com