do i need blue ray player to play blue rays or will my old player work?

A DVD player only plays DVDs but a Blu-Ray player plays both DVDs and Blu-Rays.
Some films can be bought in a 'Double Play' format meaning you get two discs: one Blu-Ray and the other DVD.
Hope this helps!

Blu-Ray discs need Blu-Ray players because they have a blue ray to read the data.
Older DVD players use red ones which are incompatible.