I replaced sparkplugs and now car is backfiring, what is the issue?

yeah it did start right up than i just went around the block 2 times than i parked it that i just was starting it up every day for the pass 4 days with out driving it that i went to drive it and it takes of very slow than it kept backfiring and did not turn over than i let it sit for about 3 hours than it started back up but i had 2 hold it all the way 2 the floor