At the bottom of each of your Rooms in Speak, you'll see a box that states "Enter your message here":
If you're only sending text, just type in your message there and hit Enter on your keyboard. Note though, that you also have the option to include attachments and/or emojis.
To add an attachment, click the attachment icon on the left of the message box. You'll then be presented with an option to browse for the file on your computer that you want to add as an attachment. Just select your file and then follow onscreen prompts for upload into the Room.
File types that can be uploaded are indicated on Twilio's website here. Note: Sprint, T-Mobile, and Verizon all allow PDFs to be sent through text message, but AT&T does not.
File size, regardless of type, is restricted to no more than 5MB in size.
Note: files such as pdfs will need to be downloaded in order for you to view them. Images, however, display inline as in some of the examples above. Further, if you click one of these inline images, they will display much larger on your screen against a black background, in order that you might view them better.
Further, for Android users of the Speak mobile app, to receive PDFs/attachments via that platform you will need to download "Messages by Google" to your device. Currently, this is the only way to ensure Android devices will receive PDFs via Speak messages.
To add an emoji, click the emoji icon on the right of the message box. You'll then see the below:
Just search, scroll or select an emoji type at the top to seek out the emoji you're looking for, select it and then click Enter to send.