First thing I would suggest is to learn chords. Why your asking? They will teach you how to position your fingers on the fretboard and give you strenght. The main reason why you're getting a buzzy sound is simple, you're forcing your fingers to perform tasks that they don't usually do. Just practice, practice and you'll get there.
You have the right approach Amar, learn and practice your riffs at slow speed. Then, as time goes by, speed them up. Focus on precision, speed will eventually come by itself. As your fingers get use to patterns and positionning, you will be able to perform those same riffs at higher speed without loosing precision.
Don't loose your motivation, you're in the hardest years. Once you get the hang of the basics then you can truly enjoy playing guitar. It's really worth the hard work.
And if you're in fact loosing your motivation. Come back to the forum. There's always someone that's been there and can help you or send me an e-mail I'll try to help out. You know, from one metallica fan to another.