change new custom sidebar to a checkbox one like the category sidebar

Good Morning,

I am working on a site on an internal server. I have successfully added a custom sidebar widget to the admin side of a post. The new sidebar is like the tag sidebar where you type in the keywords and hit enter. It is working exactly how I want it to. But I would like to try to change it to the style of the category sidebar that has check marks. Hopefully this kind will help make sure most of the new categories entered are spelled correctly etc.

Can anyone point me to the correct code or at least to some keywords to search for?

Thanks

Lisa