Go to nba.com/teams.
Click on you favorite team's website from the list. A new window will pop up.
Scroll through the topics on the team's website. These topics are similar, but each team's page is different. Be sure you're scrolling through the topics not directly at the top of the pages. These topics should be under a headline such as "Pistons.com" or "Denver Nuggets". Topics will include items such as "Tickets," "Stats," "Roster," etc. Extra windows will pop up every time you scroll over a certain topic. You're looking for a "Contact Us" option. If you can't find an option near the top of the page, scroll to the bottom of the page and look for a "Contact Us" choice.
Click on the "Contact Us" link and follow the directions on the particular team's website. Some teams will ask that you only e-mail the particular player, while others will give you the option to contact a player through the mail. Some will ask that you put the player's name in the "Subject" box as well.
Write what you would like if you're e-mailing or mailing something. Be sure to follow the rules on the team's website.