I need to configure my wireless router D-link DIR-300 for security . How do I get into my Router to protect my computer? Merlin

Here's the manual, it details everything you need: DIR 300 Wireless Router Manual

Your question is different then your title suggests. Most routers use 192.168.0.1 as the address for their configuration page. You enter http:\\192.168.0.1 in the address bar of your browser and this should bring up your router configuration. You will probably be asked for a user ID and password. The defaults for these are in your router manual.

Once in the configuration it depends on the router as to what protections you can provide. A more specific question would help.

You must spread some Reputation around before giving it to ScottGem again.