Squid config

I am fairly new to squid. I am running a test install on a bsdi 3.0
system. The one thing i'm most curious about here is how "ttl" works.
Btw, i'm currently set up as a caching only proxy. How can i adjust the
ttl on cached urls? If a page changes before the ttl expires, will the
page be updated? I noticed the default values are fairly large, for
example, currently i have the following:

 www.soonet.ca C 0 21102 1 208.128.155.2
 www.infoseek.com C 122 21391 6 204.162.96.20
204.162.96.68 204.162.96.76 204.162.96.33 204.162.96.34
204.162.96.21
 wuarchive.wustl.edu C 131 21401 1 128.252.135.4
 www.cs.ruu.nl C 139 21461 1 131.211.80.17
 ftp.sunet.se C 149 21451 2 130.238.253.4
130.238.253.5
 newton.math.psu.edu C 158 21442 2 146.186.130.5
146.186.131.193
 risc220.piaggio.cba.unige.it C 171 21429 1 130.251.107.121
 www.math.uio.no C 178 21422 1 129.240.223.53
 www.inf.utfsm.cl C 187 21413 3 200.1.19.129
146.83.198.3 200.1.19.1
 www.jmas.co.jp C 194 21406 1 133.226.128.136

Are these normal values. What kind of ttl sizes are recommended? TIA.

-- 
Don Joy
System Administrator
SooNet Corp