This is the question that so many people ask themselves before commencing lessons. Singing and using the voice is completely different from playing any other instrument because the processes involved are so intricate (the human body is very complex), that even little things like 'nerves', can alter the voice in so many different ways.
Please please, if you take nothing other than this next piece of advice from my tutor page, just give it a go!!
The lessons with the tutor (when you carefully select the right tutor) should be fun and enjoyable. if you enjoy singing, then sing!! Confidence comes as part of your rewards from practice: it isn't something you can gain overnight.