Getting Started with Lync
To log into the Office 365 portal navigate to https://portal.microsoftonline.com, enter your Office 365 email address and password, then click Sign In.
Once logged in click the Gear icon in the upper right-hand corner then select Office 365 Settings.
On the Office 365 settings page click Software.
On the software page click Lync then click Install.
If this is the first time you have signed in you will also see a window asking if you want to save your Lync sign-in info. If you click Yes Lync will automatically start the next time your machine is started. If you click No you will need to enter your log in information each time your machine is started.