The Communication tab from the Timeline displays all sent emails & texts and all manually logged phone calls or other interactions. Read more about how to manually log a new client communication here.
You can send a direct email or text message to the client by clicking on the 'Add new' button, followed by 'Communication update'.
For email types, you can type your message and add different attachments.
For text messages, you can simply type your message and click 'Send'.