As jazzmandan says, lessons and sing.
Also learn to breathe properly. I know we all think we know how, but most of us do not.
When breathing for singing or playing a wind instrument, the diaphragm should go down, the lower abdomen should extend outward, and the chest should not expand. Look at a newborn baby or a sleeping dog and you will see what I mean.
Like this.
If this isn't the first lesson your teacher shows you, get a new teacher.
If you breathe improperly you can severely damage your vocal chords, and you will never get your best singing tone.
Insights and incites by Notes.