That depends on the setup your server host provides and the software you have installed to host your site.
In most cases, you can designate a subdomain to be used as your secure site and only enable SSL for that site.
For instance, you can set up a general site, www.cool-site.com, which does not have an SSL security protocol. When you need to collect information from your visitors, you could send them to your subsite, secure.cool-site.com, where their information would be secure.