trusted keys in gpg

[Oki DZ <okidz@pindad.com>]

Hi,

I tried to send out an email using gpg (to other mine account), and in
the receiving end I had the following:
gpg: Signature made Wed Oct  9 10:03:59 2002 WIT using DSA key ID
12ACBC0B
gpg: Good signature from "Oki DZ <okidz@pindad.com>"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the
owner.
Primary key fingerprint: 4C74 27A3 EFB0 A9D5 F961  323F 43D1 FA7E 12AC
BC0B

How do you turn a key into a trusted one? Well, what is the meaning of
"trusted" in this context?

Thanks in advance,
Oki