You can use the TSO/E Information Center Facility (ICF), if installed, or TSO/E commands to send a message. For example, to send a short message (with no more than 115 characters), you can switch to TSO/E command mode and enter:

SEND 'Have to go home to take my cat to the vet' USER(alice)

You use SEND for messages to people on the same system as you.

For a longer message, or a message to someone on a different system, you could use:

TRANSMIT dallas.alice

where dallas.alice identifies the person to receive the message: dallas is the ID of the MVS™ system (known as a node in the network) where the person works, and alice is the person's user ID. The system then prompts you to enter the message.