A Notary Public is a registered administrative government witness to the signing of your document. They do not need to read the document, it is only necessary they watch the signing of it.
If you’re in the USA, your document template will have, at the end of it, a place for a Notary to sign.
While it is sufficient to have your documents signed by 2 witnesses, some may consider it of benefit to add a Notary (essentially as a 3rd witness), if such option is available to you. We consider it recommended (in the USA) but not required.