iMessage is an integrated messaging application for all users of the Apple ecosystem. From your Mac, you can send messages to all your friends, iPhone users and, if you have an iPhone, send and receive regular SMS messages with Android users.
How to set up messages on your Mac
You do not need to use iCloud (or even have an iPhone) to use iMessage, but you will need an Apple ID. If you already have an iCloud account, the email you used to register will be your Apple ID.
Run the Messages application from the Dock, the Applications folder or looking for it with Command + Space. If this is the first time you start the application, you will be asked to log in. If you do not have an Apple ID, you can click on "Create a new Apple ID" at the bottom to sign up. Otherwise, log in with your current Apple ID.
After logging in, open the message settings by clicking on "Messages" in the menu bar and selecting "Preferences" or by pressing Command + Comma.
In the «iMessage» tab you will find the options to manage your iMessage account. Make sure your phone number or email address appears in the "You can be located to receive messages on" list, or you will not receive any messages on your Mac.
If you have two contacts, such as your Apple ID and your phone number, you can receive messages in both accounts. At the bottom, you can choose which one you prefer to use when sending messages to new people.
iMessage based on an email
Using an iMessage account based on email is the same as using a phone-based one; You can send messages to anyone who uses iMessage, including your phone number. But only telephone accounts can send messages to Android users via SMS.
Before closing this window, you must make sure that the option «Enable messages in iCloud» is enabled so that all your old messages are synchronized with your Mac correctly. You must enable it on all your devices.
In case your number does not appear
If your phone number does not appear in the Messaging preferences, you will need to make sure that iMessage is enabled on your phone. Go to Settings> Messages on your phone and make sure iMessage is on. If not, you will see "Use your Apple ID for iMessage", in which you must click and log in with the account you are using on your Mac.
After everything is enabled, your phone number should appear in the Messaging preferences of your Mac in a few minutes, after which you can use iMessage as you wish.
If you want to send and receive SMS messages – this will allow you to communicate with Android users and with any other person who does not have Apple iMessage – you will also have to enable Text Message Forwarding for iPhone, and link your Mac and the other connected devices.
You will have to use FaceTime if you want to make audio or video calls. FaceTime is a standalone application, but it has a similar configuration process.