Yes, God does care what you do with your life and He doesn't want you to waste it. The reason He cares what you do with your life is because He loves you and wants what is best for you.
This is why the most important advice I can give you is to seek God's will about your future. God has a plan for your life - so why not seek it? This doesn't mean God will reveal everything to you all at once - but He will reveal the next step to you, and that's all you really need to know.
How do you find God's will? First, put your life into His hands by turning to Jesus Christ and committing yourself to Him. When you do, you become a child of God - and God becomes your heavenly Father. And because He is your heavenly Father, you can come to Him and ask Him to help you as you face the future. Jesus said, "If you... know how to give good gifts to your children, how much more will your Father in heaven give good gifts to those who ask him!" (Matthew 7:11).
Pray, therefore, about God's will for your future. Study the Bible also, to learn what kind of person God wants you to be and what He wants your goals to be. In addition, seek the advice of others who know you. Then step out in faith and trust God to guide you, even if the way seems unclear.