Size content to viewport Issue

Hello Team,

I have a website which was very slow and i used W3 Total Plugin to reduse the page load speed bu now when am checking my site in google page speed am getting issue with

Size content to viewport

The page content is too wide for the viewport, forcing the user to scroll horizontally. Size the page content to the viewport to provide a better user experience.
The page content is 500 CSS pixels wide, but the viewport is only 320 CSS pixels wide. The following elements fall outside the viewport:
The element SIGN UP falls outside the viewport.
The element <video id=”covervid-video” class=”covervid-video”></video> falls outside the viewport.
The element <h1>Need a job? T…us your story</h1> falls outside the viewport.
The element Create a Profile falls outside the viewport.

Am not that knowledgeable with WP

Can you please let me know what to do in order to fix this issue and make my site mobile friendly.