I would like to make homemade Ketchup, how do I prepare the tomato?

You will want to remove the skins. Make a small cut on the bottom of the tomato and then drop into a pot of boiling water for 30-60 seconds. When the small cut expands to a large split, remove from the pot and drop into ice water. The skins will slide right off.

You will also want to remove the seeds. You can do this by cutting the tomato and digging them out with your finger. Cook and process as usual. You can "cook the tar" out of the tomatoes until they completely break down into nothingness leaving a ketchup like substance,.

+OR+ you can cooked mixture with whole unpeeled/seeded tomatoes, THEN through a food mill or press through a fine mesh sieve. A food mill and sieve should also catch any seeds and skins.

Edited to clarify.

Roasting the whole tomatoes, seaoned and cut into halves, perhaps with some unpeeled garlic/rough chopped red onions/herbs (the first I would say is essential), then passing the results (after picking out the extras) through a seive or conical strainer, rubbing through the pulp with the back of a wooden spoon or spatula- creating a passata- can give a much deeper taste than fully preparing before cooking.

Plus it's way less fiddly. :)

If you use tomato paste the job will be faster, but I don't think it's a good idea to try to make it smooth, the texture will stay but you might be able to whip it in the blender.

Try a reduction of the watery part of the tomato. From memory here's the Heston Blumenthal recipe for this,

Ingredients: 3kg ripe, on the vine tomatoes.

• Halve the tomatoes;
• Scoop out the insides (seeds, juice and the jelly-like part in the middle) into a strainer set over a sauce pan;
• Push as much liquid through the strainer as you can using a ladle;
• Set over a medium-to-high heat and reduce until you get a ketchup consistency;
• Keep the liquid on the move with a wooden spatula to stop it from burning on the bottom of the pan;
• Taste before adding any additional sugar, it might be sweet enough without.

I usually peel the tomatoes beforehand and save the tomato meat for soups and sauces.

Better to select the fully ripped tomatoes which will get easily cooked. We can run through a kitchen hand rotated strainer which will,remove the seeds. The presence of seeds alter the taste, so they have to removed.Addtion of Tamarind, garlic, suger ( or sachrin, or artificial sweetners),ginger etc are personal choices.