You can copy an existing campaign from one account to another by following this structure. First, you have to select the account containing the campaign you want to copy from the left-hand side navigation. Next, in the Summary Grid, you have to click the Campaigns tab, then find the campaign and copy it by right-clicking on it and selecting Copy. Now, in the left-hand side navigation, you have to select a different account then right-click on it and select Paste. This will copy the entire campaign with all ad groups and ads to the new account.
This question is a part of the Microsoft Advertising Certified Professional exam. You can find all the answers with detailed explanation for this exam in the Microsoft Advertising Certified Professional exam page.