The quickest way to learn Microsoft Lync is by going through the Lync quick reference guides

IM, Presence and Contacts (.pdf)

Accept an IM request
Set or change your presence
Find someone
Add a contact
View a contact card
Create a group
Send an IM
Add audio, video, sharing, to an IM conversation
Switch between tabbed conversations
Find a previous conversation

Meetings (.pdf)

Join a Lync meeting
Schedule a meeting
Set meeting options
Record and play back
Share desktop or program
Share PowerPoint presentation

Sharing and Collaboration (.pdf)

Sharing sessions
Share your desktop or a program
Start a group IM conversation
Share a whiteboard
Transfer a file
Start a unscheduled conference call

Video (.pdf)

Use video controls and view
Manage the participants
Full screen view
Set up your video device
Start a video call
Start a video conference
Answer a video call
Invite other people to a video call
Add video to an IM conversation