You will be your first vocal teacher. Sing in the shower. Sing in the car. Sing wherever you feel comfortable. Focus on pitch and timing. Practice songs you can sing well, songs that are easy for you to sing. If you play another instrument, accompany yourself. The more you practice, the better you will get.
Once you know you enjoy singing, find a comfortable chance to do it in public. This might be with a local glee club, church choir or karaoke at a bar. If you're singing in a group, you will learn a lot from the director and from the more experienced singers. And if you're on your own at karaoke night, don't be shy to compliment those who sing well. Ask them how long they've been at it and whether they have any tips for you.
There are piano teachers, guitar teachers, drum teachers, and yes, voice teachers. Singers in particular keep vocal coaches throughout all stages of their careers. Voice teachers can teach you to recognize and take advantage of the nuances in your voice. They can help you improve your tone and technique and get the most of every performance.
Throughout every phase of your singing, keep in mind that your voice is an instrument. Know what's good for your voice (water, hot tea, lemon, honey) and what's bad for your voice (dairy, alcohol, smoking, talking loudly in noisy clubs) Do what is good and refrain from what is bad.