Hi @quyetnt2017,
You will find theme files, demo content and documentation in the zip of files you downloaded from themeforest.
Please extract it and open documentation, you will find step by step process to install theme there.
To summarize:
– Extract files you download from themeforest
– Login to wp-admin
– Go to Appearance >> Themes and Add New themes
– Upload blog-way-plus.zip and activate it.
Hope this will work.
Thanks.