Step 1:
Star with going to www.office.com to reach the Office 365 homepage. From the office 365 homepage click on the outlook application to access Outlook's settings.
Step 2:
From the office inbox menu, click on the gear symbol on the right-hand side of the page, for outlook settings.
Step 3:
Once in outlook settings, click on the link "View all Outlook Settings"
Step 4:
to get to the signature option from main outlook settings go to:
A. Mail
B. Compose and reply
Afterward, save changes and you are set to have your own personal signature from the Outlook web application.