You are Normal!
We ALL sucked when we started, everyone does. It takes a good while to develop you own system, so keep your eyes peeled for ways to make it work for you. First, is get out of the office quickly as you can. We'll all want to know a few basics:
Do you drive your own vehicle (POV)?
Does you office have lots of Amazon?
Is the route's regular involved in helping you succeed?
Try to get your Regular to order an extra set of casing stickers. If you can snag a huge box, fashion a mock-up case at home with those spare labels and stare at names, addresses. Get a Line of Travel, 4003 form and follow it on Google maps.
If you route is long and rural consider taking the DPS (letters) with you and working them on the road. Maybe transfer to short trays.
Case flats in a way that works for you, possibly larger things first, then smaller.
Do you pull down the flats into tubs or trays? Criss-crossing by address will sometimes help.
Buy cheap colored cardstock paper at a hobby store and cut into 3-4 inch strips to use for package markers. Use one color for big boxes, another for smaller things that will fit into box. Some people use 3 or more colors that mean something to them.
Learn how to check Package Lookahead on the scanner. Escape-P. It is not always perfect, but can give you an idea. Sometimes addresses show up that have no package, though.
Get your spurs (small things) into delivery order, keep within eyesight if possible, and glance over regularly. You'll still need markers in the beginning, but may someday be able to phase those out.
You'll get lots of help. Its like drinking from fire hose at first. Only those that seek to educate and learn succeed. You're already at that step.