+l = limit (sets max user limit for channel)
+p = private (channel is not visible in /whois but visible in /who) and is "obsolete"
so people rather use +s = secret, which hides channel in /whois and /who (but not from opers, just from regular users)
as noone told you how to use "room" modes:
/mode #channel_name +/-mode
example: /mode #mirc +s
+ sets mode
- unsets mode
if it is channel mode for user/host (ban, op, halfop, voice or userop)
then it is /mode #channel mode user/host
--- ban example ----
example: /mode #mirc +b *!*@stupid.spammer.com
or /mode #mirc +b idiot
--- op example ---
/mode #mirc +o my_friend
for multiple ops or voices or whatever...
use /mode #channel +ooo nick1 nick2 nick3
(depends how many modes = how many users)
you can also combine modes :P
/mode #mirc +stn-cl
which sets "stn" modes ON and unsets "cl" modes OFF
:P