Open a new email message.

On the Message menu, select Signature > Signatures.

Under Select signature to edit, choose New, and in the New Signature dialog box, type a name for the signature.

Under Edit signature, compose your signature.

Under Choose default signature for new messages select your signature, for replies is you want to use the same signature select the signature name or create a new signature.

On Outlook for Mac
On the Outlook menu, select Preferences.
Under Email, select Signatures.
Select Add to add a new signature
In the Signature editor, type the text that you want to include in your signature.
After you are done creating your signature, close the editor window

Under Choose default signature for new messages select your signature, for replies is you want to use the same signature select the signature name or create a new signature.

close the Signatures window.