Types of input signal of a BJT
(assuming small signals)
If you have a current source, you supply a current, and the base voltage will assume whatever voltage is needed to accept that current.
If you have a voltage source, you apply a voltage, and the transistor characteristics and the emitter impedance work together to form an &quot;input impedance&quot; which allows a certain base current depending on the input voltage.
At the output side, you get a current according to beta (from input current, A/A) or transconductance (gm, from the input voltage, A/V).
Then the load resistances on the collector (Rc) determine the voltage Vc according to that current Ic.
Vc = Supply - Ic * Rc.
There is no difference between output current = input current * beta, or output current = input voltage * transconductance : they are just front view and side view of the same face.
(Large signal, e.g. if the voltages exceed the supply rails, get messy. Ignore them until you have a handle on small signal behaviour)