Please note - this article pertains to our COM add-in for Outlook, not the O365 add-in for Outlook.
1. Click on New Items-->Meeting
2. Click the "Sync to Salesforce" icon in your Outlook ribbon.
a. Select the correct contact or lead in your Salesforce account
b. Select the correct account or opportunity in your Salesforce account.
The Calendar event will be associated with the selected Contact/Lead or Account/Opportunity.
You can learn more here: http://www.yesware.com/blog/calendar-sync-for-outlook/