To compose a message in Gmail, just click on the button on the upper left side of the screen:
The compose screen is below. Note that Gmail continually saves your draft message -- if your screen freezes or you lose power, there is a good chance you’ll find your message in the Drafts label.
If you click on the A you will see this menu ribbon (text formatting options):
If you click on the paper clip icon (above), you will be prompted to insert a file.
If you click on the + icon, you will see this menu...
This ribbon lets you insert a file; insert a file from Google Drive, insert a link; insert an emoticon, insert a calendar invitation; and send the message to trash...
When you are finished composing, click Send. Your sent message will be stored in Gmail’s Sent folder. To Save your message to work on it later, click Save. The message will be stored in your Drafts folder.