Time for me to ask a dumb question, 25 years after studying cryptography in university:

When I try to verify signatures using gpg it's not fully successful, and therefore I'm just accustomed to ignoring it

I guess it's because I haven't told gpg that there is any public key that I can mark as being genuine

How do I fix that? For example, if I met you at a conference and you gave me your public key, how could I tell my gpg that I trust that key?