This is a brief overview that describes equipment and techniques.
These tips will help you get started. There is a lot more to this than these tips.
For this technique you will get the best results using a quality tripod and a nodal tripod. This type of head does not tilt up or down. The nodal point of the lens can be set by sliding the camera along a rail. Shoot your images so that they overlap by 1/3rd. That overlap allows the images to be stitched together.
Start by using wide angle lens, like a 35mm lens. Later on you can use any lens… fisheye to super telephoto.
Even if you cannot see the horizon you should place the horizon in the middle of the image. Level the tripod head and spin it around assuring that it is level in all directions level. If it's level then it's aligned with the horizon.
If you are not level and pointed at the horizon and the camera is pointed upward or downward then there will be an arch in the image.