Jenta: You do need some sort of amplification unit such as a receiver or integrated amplifier. You can't simply plug your speakers into your DVD player.
Not knowing your budget, I would guess that you are purchasing generally entry level gear and I would strongly recommend that you check Costco and see what they have in the under $150.00 range (they often have some good deals on home theater receivers). Also, the Best Buy house brand Insignia has a nice home theater receiver in the under two hundred dollars bracket. (I actually bought one when they were on sale for $89.00.) And it's actually not a bad little unit.
If you really want to make your Bose speaker system sing, I'd suggest that you get into something in the 80 watt plus category. (Not hard to do these days.)
Also, don't forget about good used gear. Your $$ can go a lot further in the use gear department. Perhaps a nice powerful Yamaha receiver that sold new for over $1,000 dollars could be found for about $275.00 or less?
Best of luck!