Menu commands (right click on the window):

Load URL...: loads the specified webpage/address
Bookmark: Adds the current page to the list or loads a bookmark
Home: Loads/Sets the homepage
Recent: Loads the specified recent page in history

"/" Commands:

/www [URL]: Loads the specified URL
/www.initiate: Initiates CSBrowser

Warning:

mIRC will be greatly lagged and unusable when pages are parsing and being presented in the browser window. Once the page is finished everything will go back to normal. The lag time may be long or short depending on the size of the URL being loaded.