What they've all said! Lots of good advice is posted already--you won't go wrong following it. Also...

Listen to any infants and toddlers you may have in your life. Have some fun with them by copying pre-verbal sounds they make, using your regular speaking range as well as going higher and lower. Make a copy-game out of it. Yes, including crying sounds. It's all part of developing lung capacity and the voice.

Singing rounds is a great tool especially when you can do it with someone who someone who doesn't take it all too seriously. Row Row Row Your Boat, Frere Jacques/Are You Sleeping, Fire's Burning...lots to choose from. As a beginner, the concentration needed to keep track of your own words and notes can help to distract you from nerves and self-judgement. Best of all, sooner or later the song breaks down into roars of laughter as concentration fizzles and you both get notes and words mixed up. Laughter is good for your breathing!

Meanwhile you won't even notice how it helps you get a feel for intonation and for staying on your note while there are other notes being sung around you.

Most of all, just sing. Many times my voice sounds scratchy and feels rough to start with, until I've been singing for at least a few minutes, sometimes many minutes. After the phlegm gets flung off my vocal folds the sound is much clearer.

~CH.