What type of fuse do i need for my car?

i am using a 2007 dodge caliber with a 12 volt battery. i purchased 2 sony xplod 10 inch speakers(max 700watts) with a 600 max watt amp. i have only used my speakers for a day and then i found out that they wernt working anymore and my amp was really rally hot. i was worried the amp overheated but then i found out it was the fuse that was the problem. it blew out and i was using a 20 watt or volt fuse. then my friend came over and gave me a new fuse, this time it was a 25 and he said that it should help more than the 20, but he told me the problem was that my power cord was too thin so it would cause my amp to heat up quick if the volume was high. but my other friend tells me the thickeness of the power cord had nothing to do with it but it was just the fuse. CAN SOMEONE PLEASE TELL ME WHO IS RIGHT OR WHAT IS THE PROBLEM?