Where should I put the Portal log-in link on my website? and what should I call it?

The best place is in your website Header so it's accessible from every page on your site.  If you can not alter your header, then the Home page and any Registration pages should be used. Make it noticeable and encourage your clients to use it often to manage their account. 

You can label the link anything you'd like. View some various Parent Portal Login names and labels on the Link to Your Parent Portal page.