Go to your Outlook online using this link (skip this step if you are already on Outlook Online)

At the top right of the screen, click the Settings Cog

Click View all Outlook settings at the bottom

Under the Email tab, click "Compose and reply"

Give the signature a name, paste it in and edit in your name and job title.

Click Save at the bottom right

Once you have clicked save set the signature as your default for New Messages and Replies/Forwards and click Save again

That's it!