How to create password access in TP-LINK ADSL modem?

salam guys...i hve a TP Link TD-W8920G ADSL modem ....can anybody tell me hw can i password protect it so that others cant access my DSL without the pass...i hve found the security feature in TP-LINK home page but dnt knw how to create password for it??? kindly help me....any TP-LINK user????

also my tp-link(W89020G) ADSL modem behaves very strangley to me...sometime it connects to net n sometimes not....it depends on my luck bcoz when i supply power to my modem sometimes it starts working(by working i mean my net) n sometimes i wait n wait n wait n so on....i dnt think i hve mess with the modem settings bcoz then i wouldnt able to connect the net....n i think my service provider has no problem bcoz my net work fines on Belkin modems....now help me wat to do???