Just realized you can "like" posts....oh, dear.
You want to get the tank cycled, first. Here is a quick list of things you need to do:
Cycle the tank. Fishless takes a while, but is effective. Seeding with someone else's filter media or sand is super easy and relatively fast to do.
Make sure the tank is cycled. Do not rush stocking the tank with livestock....trust me.
....is your tank cycled?
Good!
1. Get a heater and choose stock. Is the tank a 40 breeder? I will continue as though it IS. 40 breeders are wide, and have a rectangular look to them. They can house most of your basic schoolers and fish that stay within the 1-3" range. Having said that, there are also species, room, water quality, water parameter, and tons of other variables to contemplate when stocking your tank. Trust me, you will rehome and/or kill a ton of fish if you do not do your research. Just because someone or aqadvisor says your stock is okay does NOT mean it necessarily is. Don't put African cichlids with turtles in a 40g, or do something like a red bellied pacu.
2. Should be number one, but get a liquid test kit by API or suitable. Fantastic device for measuring your water quality, which is a must.
3. I would recommend sand for your tank, depending on stock, but gravel is also fine. Sand is IMO easier to clean and more natural for your fish. I do, however, use rounded stones in my large display tank for aesthetics, along with play sand. Pool filter sand is fantastic stuff, and does not need as thorough a cleaning before installing in the tank.
4. Easy plants that are fun to look at are anubias and swords. I have broad leaf anubias, moss balls of sorts, and Amazon swords in my 40g low tech planted, and they do just fine with stock lighting and sand.
5. Don't put on lotion or antibacterial sanitizing product before cleaning or going in the tank. It'll kill everyone. Someone here lost a whole tank because of it.
I know it's a lot of info, and I just got off work, but I want to help you do this right.