Most commonly, a Power Bank will have a dedicated input socket for receiving power. This power can come from a USB socket on your computer, but may charge faster when using a wall socket adapter. We most often see Power Banks use a Mini or Micro-USB socket for charging, and full-sized USB sockets for discharging. On very rare occasions, Power Banks can use the same socket for input and output, but this is rare and should not be assumed of any Power Bank, as trying to force power into an output can damage the battery. Always check the manual for specific instructions if you're not able to find a clearly marked input socket.
Depending on the capacity of the Power Bank and its current charge level, it can take quite a while to fill up. For example, a 1500mAh rated Power Bank should take about the same time as your typical smartphone to charge. For larger banks, this time can be doubled, tripled or quadrupled. Most Power Banks have both an LED indicator to show when they are at capacity, and a safety cut-off to prevent overcharging and overheating. Whenever possible, remove the Power Bank from charger when it is full, or at least avoid leaving it connected long-term after its full. Ambient temperature and power flow will also affect charge times, so it's best to keep it topped off regularly.
Some Power Banks don't work well with high-capacity chargers (like the ones that come with iPads). Trying to fast-charge a Power Bank from a 2A charger can result in damage to the internal circuitry.