is it good to first practice heavy metal songs and things like that? or should I learn the basics of the guitar first?
you should learn the basics regardless of what you want to play. but practicing metal songs at the same time can't hurt. just don't get into thinking that metal is the be-all and end-all of guitar playing
well you should learn basics of course, but at the same time, basics are very boring. So, it may be that you'll become a better guitarist faster if all you do is basic stuff at first, but theres more fun in constantly challenging yourself (while learning basics at the same time, of course)
Learn the boring basics first - you've got no chance of playing anything metal when you start out. You need to develop some basic attributes like finger strength, callouses, fretting and picking cleanly and basic speed (as in able to change chords in less than 1 minute!). Spending a few weeks getting used to the instrument like that means you'll learn rhings far quicker.
Go nuts and have fun with whatever you want to do just dont go learning lil bits and pieces of songs, i've posted this in other places i know, but really it gets you nowhere