When you create a signature, Outlook places it in the Signature for new messages list. Simply start sending new messages. Your signature will automatically be inserted in the message.
If you wanted to send messages without a signature, you would click <None> in the Signature for new messages list. (You'll see in the practice session how to open that list.)
Even if your signature is inserted in a message automatically, you can modify the signature for that particular message. You would just select the signature text and type what you wanted. For example, you might want to use a different complimentary closing or none at all. If you wanted to delete that message's signature, you'd select it and then press DELETE.
To modify a signature and have the change apply to all messages, you must start the same way as when you create a signature. When you reach the Create Signature box, select the signature you want to change, and then click Edit.