By default (power-ON) the opamps stages biasing point is at a 0 offset from the GROUND of the circuit. This will be the most useful mode of operation as it yields full unidirectional output range for DC measurements.
You can enable bidirectional mode by tapping the uA & mA touch-pads simultaneously. This effectively switches to half-supply biasing of the op-amps, and enables the output positive [+] terminal to swing both positively and negatively WRT to the [-] negative terminal. This allows measuring AC currents and shifts the output range to [+/-1.65]A. This mode is similar to the behavior of EEVBlog’s uCurrent which has a fixed bidirectional mode.