My question is why the cd s are with cd-r or cd+r what is the difference?

I think that it means, cd+r is re-writable and cd-r is write once only

CD-R are write once discs only whereas CD-RW are re-writable discs where W is for re writable. As far as +R and -R is concerned I am not aware of CD+R if it is available. DVD are +R and -R.Some players may support only either of the two DVDs while other players may support both. If you see the specifications of players it is specifically mentioned on most of them what types of CDs or DVDs they support. Most of the players support DVD-R.