@feruze-- Yes, most jello is not halal because it is made with gelatin. Gelatin usually comes from pig fat. Even if it's from another animal, the animal was not slaughtered in the Islamic way. So just don't eat jello and avoid foods with gelatin in it.
Packaged foods without meat are usually fine though. And there is always ingredients lists on the packages so you can check to see if any meat, pork or alcohol was added. If you have a Middle Eastern / Islamic grocery store nearby, you can do your shopping from there as well. Their products are almost always halal.
The other option is kosher food. Kosher is actually same thing as halal. Maybe some religious authorities might disagree with me but Jews also require the same slaughtering methods Muslims do. And many grocery stores have kosher food, like kosher hot dogs and so forth. I personally eat kosher foods a lot.