An email signature is a block of text added automatically to at the end of an email message.
It generally includes the sender's;
Name and surname,
Title and company that he is working in,
Call to action landing social media channels or website
Click Settings in the top right.
You will see "Signature" section, click the option,
Add your signature text to the box (you can also format your email signature by adding an image or by changing the text type),