A reef tank is one of the coolest things you can have in your home, and it's not as scary as it looks if you start out the right way.
The biggest thing is keeping your water stable. Coral don't like surprises. Keep your salinity, temperature, alkalinity, calcium and magnesium steady, because big swings stress coral and slow their growth. Get a good test kit and stay on top of your maintenance.
Lighting matters a lot. Most reef coral have tiny algae living inside them called zooxanthellae, and those algae turn light into food for the coral. That's why good lighting is key for both health and color. Most people run LEDs now so they can dial in the brightness and spectrum. Some coral want strong light up high, and others do better lower down near the sand, so check what each one likes before you place it.
You also need good water flow. On a real reef, moving water brings in food and carries away waste. At home, powerheads and pumps do that job and keep junk from settling. Just don't blast coral directly, because too much flow can tear up their tissue. Mixed, indirect flow around the tank is what you want.
If you're new, start with soft coral like mushrooms, zoanthids and leathers. They're more forgiving when your water isn't perfect. Once you've got some experience and your tank has matured, you can move up to LPS (large polyp stony) and SPS (small polyp stony) coral.
Aquascaping is the fun part. How you stack your rock and place your coral gives the tank a natural reef look, gives fish and inverts places to hide, and adds depth. Leave each coral room to grow, with the right light and flow.
Last thing: be patient. Reef tanks grow slowly, and rushing changes is how problems start. Keep your water steady, get your light and flow right, and pick the right coral, and your tank will keep getting better every month.