Hello, welcome to the forum. Some skins, such as the default skin "Custom," already have a calendar displayed in the sidebar. If you're using a skin that doesn't have the calendar, it's not too hard to add it. You can look in /skins/custom/_main.php and find the code for including _calendar.php and copy that you /skins/yourskin/_main.php . You'll also need to copy the actual _calendar.php from the custom folder to the folder for the skin you're using. I'm assuming you're using b2evolution version 0.9.1 . If you're using 1.6-alpha, it's a little different.

Thank's a lot, i have find a solution upgrading to 1.6-alpha and changing the skin of my blog.