CTA stands for call to action. A call to action is a button (or simply a text link) that tells site users to do something—explore the site further, fill out a contact form, browse a portfolio etc. CTAs are important for two reasons: first, they can be used to drive people into a page where they become a conversion—whether that means contacting you, buying something, requesting an estimate, or something else. Second, CTAs help increase your click-through rate, which is the number of pages an average visitor views when they visit your site. Website visitors should be exploring your site, clicking around and viewing many pages, not just visiting a home page or contact page and then leaving. This is important to your SEO because a high click through rate makes your site look reputable to search engines.
To get more people to click on your CTAs, make them large, place them prominently on the page, and make them visually attractive. They can be set apart from the rest of the page content with some white space or another visual element.
Your web developer can run analysis and A/B testing to find out how effective your CTAs are, and whether changing the color or position of the CTA can increase click through rate.