You may sing or whistle (the latter might work better). When singing, please don't sing with the actual lyrics - rather, sing every note on the same syllable. Make sure you see a reddish bar moving around underneath the "Record" button while recording. If you don't, check your microphone settings. If things still go wrong, click on "Debug Information" and check the chart that will visualize your sung query with green bars, and try to sing in a way such that your melody is actually recognizable in the chart. Also, you can delete superfluous notes, and move notes around. Play the recognized melody to check it.
