I have transfered some music to my phone from my laptop but there is a red mark by each tune and when I try to play it it says cant open file have I done somthink wrong

Simply use a data cable to connect your phone and computer. Once connected, pull down notification bar, you should see USB settings, choose Media device (MTP) or USB storage.

I also use an app called AirDroid, you can easily transfer files from your computer to phone via Wi-Fi.