Your landing page is where people go after clicking your ad. You select either the Final URL or Destination URL and then enter the URL of your landing page.
The final URL is an upgraded version of the destination URL. It allows you to define a mobile URL and a tracking template and custom parameters for URL tracking. To learn more, see What are Upgraded URLs and how do I upgrade?
Generally you will define a default landing page for each ad, but then will often provide additional specific destination URLs for certain keywords. These keyword-specific URLs take searchers to landing pages that are particularly relevant to those keywords.
Your landing page is the first impression of your business that a customer gets after clicking your ad. You want to make that a good first impression! Your landing page should load quickly, include original content and have the information the user is searching for.
Your landing page also impacts your quality score, which in turn impacts how often and where your ad displays. To help ensure a high quality score, it's important that your landing page is relevant to keywords that trigger your ad and that it follows Microsoft Advertising policies.