Trying to use a tuner on your voice is a recipe for tears.

If you're *really* starting from scratch, you need to learn to match single notes. You can do this against an instrument but a better starting point is to find a willing victim, ideally of the same sex, and ask them to suffer it for your sake.

Once you've done that you can sit with a guitar or keyboard and try to match scales or arpeggios but that initial learning to recognise and key into a reference note is, well, key.