How to redirect user who visit the site directly except those who use a hyperlink to visit the site?

How to redirect user who visit the site directly except those who use a hyperlink to visit the site?

Can someone help me with this.The main goal is we have a site that selling greeting cards. we have step by step process that include visiting site one step at a time. what if the user visit the site directly without visiting the the main site. the idea is the user will be redirected to the main site. the simple solution is using meta that will redirect the user but the problem is it also redirect the user who use the main page. 

Thanks!