On your league's website, navigate to your team's home page. The path to your team page may be different depending on how your league configured their site, so the easiest path may be to click on your team name on the league standings page.
On your team home page, there should be a Calendar module. In the lower right hand corner, you'll see an 'ICAL' icon. Clicking that icon will produce a pop-up window with a iCal feed URL. Copy that URL and then enter it into your team page.