If you want to propose a trade, select "Propose Trade" from your Team Page. Then we email the other manager with your offer, which also shows up on their team page.
To discuss other general issues, a number of options exist.
On the Email League page—linked from the League Overview—you can compose an email and send it to one or more managers, all from within the game; you don't need to open your regular email application.
On the Managers page—also linked from the League Overview—you can find the Yahoo! ID and email address of the other managers in your league. You can use these to send email or chat via Yahoo! Messenger
Both of these options require that the other manager has chosen to make their contact information public. If you'd like to contact a manager who doesn't list their contact info, try posting a message on the league's Recent Messages board. This is a great place to discuss fantasy hockey issues with the other members of your league.