There are many different ways to can tomatoes. The method one chooses can depend on desired effects and length of time one needs to preserve them.
One easy way is to put the tomatoes in a canning jar. Then fill the gaps up with water. Now boil the can in a water bath canner for 40 to 45 minutes.
Another method involves taking tomatoes from frozen. Then first defrost these pre-frozen tomatoes, and follow the above steps.
When one does not have a canner, sterilize the mason jars by boiling them. Then boil the actual tomatoes, take off the peels, and add to the jars. Squish these tomatoes down and add more. Now to fill up use lemon juice. Then screw on the lids. Always make sure if the lids rise up to push them down. This prevents bacteria from growing in the jars and the tomatoes from oxidizing.
Whether canning tomatoes with all the gear or just a large pot, there are so many recipes that will call for these canned tomatoes year round.