Utilize the Chat feature to instant message a colleague

Watch a video on inviting someone to chat in Gmail.

Before you can chat with someone using a Google Chat property (i.e Gmail, orkut, Google+) you'll need to invite them by following the instructions below. Your friend will see the invitation above their chat list asking if they'd like to be able to chat with you. Until they accept, you'll see 'Invited' next to their name in your chat list.

Once they've accepted your invitation, you'll see a status button to the left of their name in your chat list, which indicates whether they're available (green), busy (red), idle (yellow), or offline (gray). At that point, just click on their name to send them a chat message.

To invite someone to chat:

1. In the search box at the top of the Chat area, type your friend's username. If they're already in your Contacts, Gmail will pre-populate their username.
2. Click Invite to chat.

If you invite someone who doesn't use Gmail or Google Talk, we'll send an email asking them to sign up for one of these products.

Learn how to invite AIM users to chat

Google+ Users: If you invite someone to chat who isn't a Google+  member yet, they won't receive an invitation to join Google+. (You can invite them to join Google+ from the Find people tab, or by choosing to share something with them.) If that person does join Google+ and adds you to their chat list, you'll be able to chat with them.