All Gnutella does is search. Once the results have been found and the sharer's IP address has been acquired, your servent then:
1) Establishes a direct TCP/IP connection withh the sharer.
2) Sends (directly to sharer) an HTTP request that looks like:
GET /get/<File Index>/<File Name>/HTTP/1.0\r\n
Connection: Keep-Alive\r\n
Range: bytes=0-\r\n
User-Agent: Gnutella\r\n
\r\n

Note that this request does not go through the Gnutella network. Note also that the resulting file transfer is direct to you through the regular internet, not through Gnutella. Gnutella is just a means to find a filename you want and an IP address who has it.

(Firewalled servents are a little different, but the file transfer still happens on the regular internet without passing through anyone else's computer)