I have a fretless bass guitar and no idea how to play. I have no experience whatsoever but I’m eager to learn. Can anyone help me out?

Not many people start off on the fretless bass ; most people learn on the standard fretted bass and later make the switch. But this should not present too many problems for you

Do you have "fret" markers on the fingerboard or is the fingerboard a plain piece of ebony, perhaps with some dots up the side of the neck ?

I strongly advise you to get some lessons for the first 12 months just to get you started. After that you may feel competent enough to keep teaching yourself.

You could start off by learning the notes on the fingerboard and playing some scales.

http://www.activebass.com/basics/fboard.asp

http://www.cyberfretbass.com/scales/primer/page2.php

EDIT : Do not learn TABS ; learn how to read standard musical notation. Buy a few books at your music store.