Okay, we’ll start with the basics.
The washing machine is the one that fills up with water, and the one that does not fill up with water is the dryer. The really tall one full of food is the “refrigerator”.

Anyway, the most important thing about washing sheets is making sure the load is balanced. You can’t just stuff all the sheets into the washer in a big wad, because when it goes into the Spin cycle they will all collect in one side of the tub and get the washer off balance and it will start going “ka-CHUNK ka-CHUNK ka-CHUNK”, helplessly teetering more and more off balance, walking itself across the floor like Robbie the Robot’s idiot cousin. Note: if you do find your washer doing the Drunken Shao Lin Master Dance across the basement floor, you stop it by simply going over and opening the lid. All washers have a safety feature that stops the cycle when the lid opens. Then you reach in there and rearrange the hot, wet sheets or towels, so they’re more or less equal around the tub, you close the lid, and you stand there and wait to make sure it resumes spinning normally. If it’s still going “ka-CHUNK ka-CHUNK”, then you have to rearrange the sheets some more, and keep at it until the washer is happy and will spin normally.
So, when you put the sheets (or towels) in, arrange them more or less carefully around the central post thingie. Don’t “wrap” them, just kind of put them in there, spread out, around and around, not in big wads or segments. Is this making sense? Pretend that you are arranging a series of feather boas around Greta Garbo’s neck. Gently drape them, just so…
Also, don’t try to wash more than four or five twin-size sheets, or three full or queen-size sheets at one time. Put them loosely in the tub before it fills up with water and look to see how far up the side of the tub it comes–it should be just barely up to the rim of the tub (NOT the outside part of the washer, I mean the tub thingie that holds the clothes and whirls around).
I wouldn’t advise you, as an amateur, to attempt mixing sheets and towels. This is a matter best left to experts. The varying weights can play merry hell with a washer’s spin cycle, although if you’re at a laundromat and you have to sit there and read a magazine anyway, and you don’t have anything better to do than rearrange sopping wet sheets and towels over and over again, until the washer gets over its snit…
Put the sheets in, select the proper setting. Anything is fine–“Heavy soil” is probably overkill unless your sheets are particularly filthy, in which case I don’t wanna know about it. “Hot” temperatures are traditional for linens, but not mandatory, “warm” works just fine. “Cold” doesn’t wash too good, but it’s fine for the Rinse cycle.
Put some laundry soap in. MEASURE! Don’t just glug some in 'cause you’ll get way too much and you’ll find yourself in the middle of the Three Stooges episode where oceans of laundry soap come bubbling up the cellar stairs. The best laundry soap IMO is the El Cheapo liquid laundry detergent, all grocery stores everywhere have a house brand, costs about $3.00 a jug. Look for it down on the bottom shelf in the Soap and Detergents Aisle, out of your line-of-sight. You can usually get away with using half as much as the manufacturer recommends, unless your sheets are unusually filthy.
Adding liquid fabric softener to the washer is a PITA, IMO. Use fabric softener sheets in the dryer, they’re more convenient. If you’re on a really tight budget, you can rip the fabric softener sheet in half and use just half a sheet per load, it’ll work fine.
You don’t really need fabric softener, whether sheets or liquid. The only reason to use fabric softener for linens IMO is if you have a big static electricity problem where you live. If you take the sheets out of the dryer and they all stick to each other with a huge crackling of electricity, then you know you need fabric softener. Otherwise, you needn’t bother. Also, towels that haven’t had fabric softener sheets added in the dryer are definitely slightly more absorbent. Scratchy, but absorbent.
Don’t bother ironing sheets. That’s why they invented Perma-Press, honey. 
Towels are the same thing as sheets, except that you have to be MUCH more careful about getting them arranged so as not to get the washer off balance. And since towels absorb water, they get much heavier when they’re wet, and are much more likely to send the off-balance washer on a cosmic trek across the floor. The limit on number of towels in the washer is, IMO, four of the really huge fluffy bath towels, or eight (8) of the smaller El Cheapo thin bath towels. I repeat, this is because of weight considerations–four big bath towels won’t look like they’re taking up that much space in the washer and you’ll be tempted to stuff a couple more towels in there.
Don’t.
Pillowcases and washcloths can be tucked in anywhere, a few at a time, in any load of either sheets or towels.
One last thing–ALWAYS clean out the dryer’s lint trap in between each load of laundry, and especially when doing linens. Towels are phenomenal producers of lint, and that fuzz really does build up and cause fires, so get in the habit of grabbing that wad of lint and tossing it in the trash.