hello when I open my mute and I speak but my teacher can't hear me

What type of device are you using?  If iOS or Android, see this troubleshooting guide:

https://support.zoom.us/hc/en-us/articles/204484835-My-Audio-is-Not-Working-on-iOS-or-Android 

If Windows or Mac or Linux, I don’t have much to go on.  Please run the Audio Test in Zoom Settings Audio tab.