The electrostatic gating defined channel in graphene forms a charge carrier guider. We theoretically investigated electronic transport properties of a single channel and an Aharanov-Bohm (AB) interferometer, based on a charge carrier guider in a graphene nanoribbon. Quantized conductance is found in a single channel, and the guider shows high efficiency in the optical fiber regime, in good agreement with the experiment results. For an AB interferometer without a magnetic field, quantized conductance occurs when there are a few modes inside the channel. The local density of states (LDOS) inside the AB interferometer shows quantum scars when the scattering is strong. At low magnetic field, a periodical conductance oscillation appears. The conductance has a maximum value at zero magnetic field in the absence of intravalley scattering. The mechanism was investigated by LDOS calculations and a toy model.