I follow the usual process of a brief immersion in boiling water followed by cold/ice water to loosen the skins. The tomatoes are then cored and peeled.
At this point you need to decide whether you want whole, chopped or crushed tomatoes. I find that cutting them (chopped or crushed) releases the most juice/water and crushed suits my needs so I run them through a few pulses in my food processor. This one accommodates a fairly large volume so it doesn't take a lot of time to process a batch. It holds up to 14 cups.
I then place the tomatoes in a colander with a container below to catch the liquid.
Once the tomatoes are strained I refrigerate the solids while the liquids go in a pot to boil until reduced by half or more. The reduced liquid will look like a light to medium body tomato sauce--not super thick. If you refer to the image labeled "reduced liquid" you will see the various levels marked on the side of the pot as the liquid reduced.
Prepare the jars as directed in your chosen canning reference guide. Fill the jars as directed in the canning materials. When canning using a pressure canner I use my All American canner. It also works for the water bath canning method. Make sure you do your research and use canning guides from a trusted source. I pressure can my tomatoes rather than water bath. Recent information states that not all tomato varieties have the PH level considered safe for water bath processing.
In addition to canning plain tomatoes and marinara I also canned a tomato soup base that will be finished with a bit of chicken stock and heavy cream for serving. The reduced liquid has a wonderfully smooth texture and could be used alone to make a tomato juice beverage. Combined with juice from other vegetables you could come up with a V7 or V9! Be sure and research canning pressure and times if you stray from using tomatoes alone.