How to paint my front door?

Exterior latex enamel. Latex is water based, makes for easier clean up and dries quickly

You don't state if your door is wood or metal. If you are dealing with wood you will need to sand the door first to remove the varnish that is on it. If the door is metal you will just need to give it a good scrubbing first. A roller will give a more even surface of paint so you don't have to worry about brush marks. I think its easier to take the door off and lay it down to paint but its not necessary.

chalk paint so easy especially on painted steel door

Agreed, I love using chalk paint- I'm excited to see how yours comes out!