Why can I hear my recorded signal only on one speaker?
When you are recording a mono source with only one channel through
one input, such as the signal from a microphone or a guitar for
example, you need to make sure to record on a mono track rather than a
stereo track in your audio software (DAW). Otherwise you would have it
only one one channel (either left or right), which you will notice when
you playback the signal.
Your source is mono, as such it cannot be recorded to more than one channel.
Because of that, basically every DAW provides the option to record on a mono
track, which should actually be the default. Of course your DAW will output
the signal through both speakers (controlled by the settings inside the mixer
of the DAW) then.
The only time you would record on a stereo track is when
your actual source is stereo with two separate channels (for example if
you record the output of a CD player or turntable).
Please consult the documentation of your DAW to check how to setup recording on a mono or stereo track.