Capacitors, from every chart I've seen, charge exponentially. Capacitors are reactive and not linear devices, so they charge in a curve, exponential way.
I read above how they can charge linearly with current. This could be right, but I know nothing about this method.
A good circuit to learn how to connect the LM386 circuit is below:
http://www.learningaboutelectronics.com/Articles/How-to-connect-a-LM386-audio-amplifier-chip
It has the diagrams and all the wiring, so it's easy to connect.