There are different types of ads and the more we understand the types - the better we can make the ad we are trying to make.
Some are introductory: introducing something new or updated with the goal of creating curiosity in the viewer.
Some are promotion based: Giving some type of offer to the client to get them to buy.
And some can be brand love based: Connecting with existing customers and reinforcing what the brand stands for to non-customers.
There are many more types and they are not set in stone but the more we can understand the types, the more clear we can be about the ad we are about to create.