First, find your range. Identify whether you have a high voice (soprano) or low voice (tenor) or somewhere in between. If you sing out of your voice range, you will never sound good no matter how much you practice. Start by seeing how low and how high your voice will reach. Determine which sounds better and which pitch is most comfortable to achieve.
Next, try matching your voice to other singers and then practice singing along with their songs. When practicing singing, sing loudly rather than softly. This builds strength in your vocal cords and strength is what will eventually enable you to control them better.
Breathing is an important aspect of singing. Draw your breath from deep down and learn to use the breath to emit the sound from your diaphragm rather than your throat or nose. With practice, your breathing will become coordinated with your vocal cords as you strengthen and smooth your vocal cords.