A CTA is an instruction to the audience in hopes of creating an immediate response. Using verbs such as "call now", "find out more", or "visit a store today" provokes the visitor to take an action after reading or viewing a video about your products and/or services.
CTAs do not have to be demanding and can simply be a polite request. When used properly, CTAs can create a pattern of behavior that assists the customer in completing a more demanding request like purchasing a product or providing personal and contact information. An example of this can be the design and purchase of a designer bag. Your website might request the visitor to choose a style, design, color, or even a personalized engraving. When the potential customer follows all the steps, they are able to see the personalized and finalized product that will make them feel even more inclined to buy. If they are able to rotate their product on their mobile, tablet, and desktop that is also very helpful.
On websites, a CTA can simply be a button, banner, or a type of graphic or text that is meant to lead the visitor down a conversion funnel. The primary goal of CTAs is to get customers to click and continue down that funnel until your desired action is carried out which in most cases is a purchase of your product or service. An effective way to measure CTAs is to utilize A/B testing where several graphics or texts are presented to users to see which one gets more clicks, and whichever one has the higher success rate becomes the default.