When I make jelly, I boil the berries(lol, I got ya know) and strain them and just mix it with sugar. With jam, you cook there berries down and add sugar to it just like that. bam.
Grasshopper walks into a bar Bartender says "hey, we have a drink named after you." Grasshopper says "you have a drink named Tim?"
Jam spreads well. Jelly just clumps a bit and when you try to spread it it rips your bread apart. Also...Jam is better to use as a cake filling or cheesecake swirl.