A call to action is the line in your ad that tells people what to do next, like "Buy now" or "Learn more." To find the best one, run the same ad with different call to action lines and track the results. Keep everything else the same so you can see which line brings more clicks or sales. After some days, compare the numbers clearly. Remove the weak one and keep improving the strong one. Which call to action style usually brings better results in most cases?