If we’re being pedantic, two photos of the same sunset, taken a couple of minutes apart.
Here’s the first:
The metering system has compensated for the bright disk of the sun by underexposing the rest of the image, so the sea and some of the cloud have come out close to black. The overall effect looks unnaturally dark, dramatic and maybe even a little bit spooky. The dark strand of cloud across the sun like the wing of a giant black bird … at this rate I’ll be imagining the spirit of Sauron rising up from Barad-dûr.
And here’s the second:
Taken from the same spot two minutes later, but with exposure compensation of +2 stops. It now looks much more like a “conventional” sunset, preventing the blacking out of the sea and lightening the areas of cloud, revealing some cute formations that are hidden in the other shot.
Personally I prefer the first picture. It’s a bit different and has more impact, even if technically underexposed.
Most people will have come across a striking sunset at some point in their lives and tried to capture it on camera. It is frankly impossible to capture the image as seen with the naked eye. The camera cannot cover the dynamic range. The best you can do is try to end up with a dramatic picture, whether it is faithful to what you saw on the day or not. Achieving that lesser aim is partly down to technique and partly down to luck. You can put yourself in the right place at the right time of day but it is really down to the weather conditions at the time. Either the setting sun is obscured or not, the cloud formations create interesting effects or not.
Beyond that, you really need a tripod so you can use slower shutter speeds and a longish lens helps to get the sun larger in the frame. Focusing should not be that difficult. The rest is experimenting with exposure and a modest amount of fiddling in post.