You can entangle two photons in a lab, keep one of them and send the other far away. For example, you can construct the pair in a way that both give the same polarization. If you measure one and the result is horizontal, then the result of measuring the polarization of the other is horizontal. If you measure one and the result is vertical, then the result of measuring the polarization of the other is vertical.
But a trick that is usually untold is that you can put a device in the path of the photon that is going far away to rotate it 90 degrees. The important part is that the photon in the lab is not affected. You can't make any measurement in the photon that you keep in the lab to check if the photon far away passed through the device to rotate it or not. But now if you measure one and the result is horizontal, then the result of measuring the polarization of the other is vertical. If you measure one and the result is vertical, then the result of measuring the polarization of the other is horizontal.
You can entangle two photons in a lab, keep one of them and send the other far away. For example, you can construct the pair in a way that both give the same polarization. If you measure one and the result is horizontal, then the result of measuring the polarization of the other is horizontal. If you measure one and the result is vertical, then the result of measuring the polarization of the other is vertical.
But a trick that is usually untold is that you can put a device in the path of the photon that is going far away to rotate it 90 degrees. The important part is that the photon in the lab is not affected. You can't make any measurement in the photon that you keep in the lab to check if the photon far away passed through the device to rotate it or not. But now if you measure one and the result is horizontal, then the result of measuring the polarization of the other is vertical. If you measure one and the result is vertical, then the result of measuring the polarization of the other is horizontal.