Local6.info is the facility (Local6) and level (Info) of the log message (Google syslog for info on facilities and levels for syslog)
The rest of that line seems to be the client IP (146.215.56.58), ecryption standard (TLSv1), encryptino level (AES256 using SHA hashing and an RSA key with diffie helman I think), and the "POST ..." tells you the method, URI and HTTP version requested via iControl returning 437 Bytes...
The crond lines are from crond (Google crond for an indepth explanation, but it runs processes at regular intervals. This one is crunning cron.hourly and doing a system check. The number in brackets after crond is the processID that was running.
The last one is a message from httpd (Apache). Telling you a user was authenitcated via PAM (Pluggable Authentication module) successfully...
Probably not a single manual for all that... Not that i've seen anyway, but syslog is your first port of call it'll explain the general syslog line format. And from that you can find which app/program is logging and find out its log format separately.
H