Petticoats aren't really that simple. Well, they're fairly simple, but extremely time consuming and a pretty big project for a non- habitual sewer.

Basically, you make a half-circle skirt (there's lots of tutorials online for this)
Rip the rest of the sheet into strips about 6 inches wide. Hand pleat and pin to the bottom of your new skirt, repeat repeat repeat. Working your way up is easiest. I don't hem the ruffles because I'm lazy. Instead I carefully pull out more threads to make a nice fuzzy edge. It's less noticeable than a hem, and much faster, but tricky to do the first few times. This also only works if you rip your fabric into the shape you want, which I always do.
After days of pleating and sewing until you can't bear the sight of another pin, you may just have the world's most lovely petticoat!

Mine didn't actually take me days, it took about a month and a half. That was only because I took week long breaks whenever I got bored, and I'm easily distracted. If I did it straight through it would take me maybe 10 hours.

Since you're a beginner, you might try making a simple circle skirt and seeing how you feel about continuing. The ruffles take a long time, but if your sewing machine has a ruffle foot this can be sped up.

I may post a picture soon of the one I made.