Some things to think about...
1. Concrete or cement products don't actually dry. They take a very long time to cure which is a chemical process. Some concretes can be cured submerged in water.
2. Which brings us to this, don't attempt a big concrete project a few days before the deadline to enter the concrete contest. It'll cure when it wants to.
3. Concrete is heavy. Getting a 50 lb bag home from the store may be a chore.
4. Concrete depends on having enough water around to cure properly. Too much or too little affects the quality of the concrete. It is as much science as it is an art.
5. The supporting structure or form should be water resistant and strong enough when wet to hold up to the concrete. Which means raw cardboard not so good. Use rigid foam cut from sheets/blocks or spray on.
6. Concrete is highly alkaline. Anything embedded in it should resist the chemicals in cement/concrete. It is tough on exposed skin. Wash with vinegar to neutralize the reaction. Wear rubber or nitrile gloves when working with concrete.
7. Try not to breathe the dust or particles from the concrete powder. Use a dust mask and full clothing.
8. Mix with power tools if you can. It is hard work.
9. When mixing or using, concrete splatters all over the place. Do outdoors where you can be messy.
10. Almost like playing with mud, a little more funner.
11. Cement is the term properly used for just the binding agents. When mixed with aggregates/stone/sand to give it strength, the mix is concrete.
12. You never want a pair of cement shoes nor do you want to deal with anyone who wants to make you some.
So what do you need to get started?
A bag of cement mix, I used the Surface Bonding Cement. You might be able to improvise with the other sand topping mixes, acrylic fortified patching cement, stucco mixes, essentially the stuff without the big rocks and gravel.
Mixing implements that will be stuck with cement residue afterwards. You shouldn't really clean up in the sink if you want to prevent any major repair clogs. Rinse off with a garden hose outside and capture runoff to dispose of properly when dried.
Plenty of newspaper and cardboard.
A heavy duty stapler or lots of tape.
Utility knife or heavy duty shears to cut the cardboard
Rubber or nitrile gloves to protect your hands.
Dust mask and safety glasses as additional protection.