You will only send the 1040 X and the supporting documents that resulted in the change. For example is you did the amendment to add a W-2, send in a copy of the W-2 along with the 1040 X
Do not include your old 1040 nor your revised 1040 because the Form 1040X reflects any changes there and becomes your new tax return.
Include any new/corrected document only if it shows federal tax withheld, and include any other Sequence Numbered tax forms that changed due to your amendment.
Attachment Sequence Number is on all the forms that come after 1040.