Character flies up and gets stuck there, won't move forward?

Hello! So I am an absolute beginner to Unity and programming in general. I've been able to figure most things out through tutorials and such, but I am really struggling with getting my character to move. I've given my character the basic 3rd person controller script that comes with the Unity Standard assets and everything seems to be working fine- no script errors, etc. But when I try to test my game, the character immediately flies into the air and comes back down as soon as I press the play button. Then when I try to control the character by pressing the WASD keys, it flies up and won't stop flying up, and cannot move forward, only turn around in different directions. Please give me any suggestions as to what you think may be wrong and how I can fix it! Thank you in advance!