For audio signals, you would normally use the exponential VCA (A-131), and for control voltages, the linear VCA (A-130). It doesn't always have to be that way, though.

The amount of amplification is determined by the sum of the voltages at the two inputs CV1 and CV2, and the control voltage generated by the manual Gain control. By means of the Gain control the VCA can be opened manually without external control voltage.
The control voltage range for CV1 and CV2 is about 0...+5V to obtain an amplification in the range 0...1.
CV2 is additionally equipped with an attenuator. This enables to adjust the level of the control voltage (e.g. when the maximum value of the control voltage is clearly higher than +5V). 

The VCA has two audio inputs, each equipped with an attenuator (kind of a miniature mixer). The sum of both audio signals is processed by the VCA according to the applied control voltages and the position of the Gain control.

The audio output is also equipped with an attenuator to adjust the output level to the particular requirements.

Remarks:
Over the years three different versions of the module A-130 und A-131 have been manufactured:
Version 1:
The first versions of A-130 and A-131 were equipped with the Curtis chips CEM3381/PA381 (A-130) and CEM3382 (A-131). These versions of A-130/131 were not able to process slowly varying control voltages as they had AC coupled signal in/outputs. They were manufactured until about 2001.
Version 2:
The second versions of A-130 and A-131 were equipped with the OTA circuit CA3080 and they were able to process even slowly varying control voltages as they had DC coupled signal in/outputs. They were manufactured from 2001 until March 2013.
Version 3:
Die latest versions of von A-130 and 131 are equipped with the high-end VCA circuits SSM2164/V2164 (A-130) and THAT2159/V2159/SA2159 (A-131). Even they are able to process slowly varying control voltages as they have DC coupled signal in/outputs. These are manufactured since March 2013. Unfortunately it's not possible to upgrade older modules because the new circuitry is totally different.

Remark: Module A-130 has been renamed to A-130-1 to distinguish it better from other modules of the A-130 series (e.g. A-130-2, A-130-8)