Create a Custom Object
Click Admin, and in the tree, select Database Management > Marketo Custom Objects.
Click New Custom Object.
Enter a display name. The API Name and Plural Name populate automatically, but you can edit them
. Enter a description (optional).
Slide the Show in Lead Detail to display Show if you want to view custom object data on the Lead Database page. Click Save.
Why wouldn't you want to see custom objects on the Lead Detail page? Well, if you created a large number of them, they could take up a lot of space.