Glossary
What is a public key?
Public keyey is the shareable half of a key pair. It cannot create signatures, but anyone can use it to check a signature made by the matching private key.
You can hand your public key to anyone, which is the point. Checking a signature needs only the document, the signature and this key.
The certificate is how a public key gets a name attached: the certifying authority vouches that the key belongs to a particular person.