Send the manuscript with the US Postal Service First Class, Special Standard or Priority. Don't ask for a signed receipt as it portrays an element of distrust. If you want to insure the publisher or agent received your manuscript enclose a Self-Addressed Stamped Post Card. Make sure you use a computer so you can deliver your manuscript on computer disk if the publisher selects to publish your book. Surprisingly, publishers do obtain hand-typed manuscripts and this can ruin a publishing opportunity for you.
All publishers can handle that program with ease.
Double-space text is the standard with one inch margins. Fonts can be 12 point New Times Roman, Arial , Courier or similar. Do not send an original. Send a photocopy or computer printed copy. Do not use any sort of binding unless otherwise instructed.