Install WordPress itself is very easy, to install a WordPress theme is even more easier by just a few clicks. All you need is login to WordPress Dashboard using Administrator user account then go to Appearance >> Themes >> Add New. Right here you have 2 options.
1. Install Free WordPress Theme by start searching for theme, those theme are stored in wordpress.org
2. Install Premium Theme by upload
If you have a WordPress theme downloaded, you can Click Upload Theme to start upload theme from your local computer. This will take your several minutes to complete, the waiting time is slow or fast depend on your internet speed and the theme capacity.
After this process you will be asked to Active the theme or not, if you select Active then you are done installing the theme.
Please commend bellow if you have success install your WordPress Theme or is there any bug you have found, any problem you ever met, We will find you an answer then.