Your logo is your main branding vehicle. It helps create and support brand recognition, so it is a good idea to use your logo on your campaigns as well.
You can upload your logo to each campaign individually, or you can upload it to the settings section to have it automatically apply to all your new campaigns.
First, click on the marketing button and then hover over settings and click on logo.
Select auto-size or original format then click on add files to select your logo file and click on the green upload button.
Now, when you create a new campaign, your logo will automatically be added to the logo area of the template.