Hi there, and welcome to the forums.
Your request is a little sketchy on details. Which log file(s) specifically are you referring to?
Before we look at how to find messages for a particular date, remember that many (most?) log files on Linux are probably rotated regularly, typically when they reach a specific size. This means all the messages for a particular date may not be in a single file; they may be spread across 2 or more files. On my one machine for example the main /var/log/messages log file rotates every 2-3 days, and did so yesterday, so the messages for yesterday are spread across /var/log/messages-20121101.bz2 (the last archived & compressed file) and /var/log/messages (the current file).
Assuming the log files in question are written by the syslog deamon, each message should contain a date & time stamp. The actual format of the date may vary depending on your distro & localle, so check the file for examples. On my machine I can find yesterday's messages in the current log by running:
grep '^Nov 1' /var/log/messages | less
I can do the same for the previous (archived) file with:
zgrep '^Nov 1' /var/log/messages-20121101.bz2 | less
or combine the two with:
(bunzip2 -c /var/log/messages-20121101.bz2 ; cat /var/log/messages ) | grep '^Nov 1'| less
I hope this helps. Good luck!