I learned how to can tomatoes from a co-worker and this is my second year doing it. She said you need to skin them. The best way for me is to put about 8 tomatoes in a strainer and dump boiling water over them to scald them. Most of the time I can then just peel most of the skin off with my hand. I make sure to core them and pull out some of the seeds. Then slice em up, put them in the pot with some canning salt and let them boil for awhile to reduce them down.
Good luck!! I am going to a Farmer's Auction tomorrow where I can buy fresh fruits and veggies being auctioned off. My friend go 20 lbs of tomatoes the other day for $3.