Lipos are charged in two phases called CC/CV

Phase 1 or Constant Current
Battery is fed full voltage (specified cells) at the full current rate you specify

Phase 2 or Constant Voltage, activated when a cell hits 4.2v (some a little lower)
Voltage held steady and current tapered off until all cells are all at 4.2v
Bleed current is used to stop the weaker cells from being over-charged while the others catch up

Cycle terminates when cells are balanced and charge current drops to a percentage of user inputted charge rate (usually 1/10c but some are adjustable)

Fast / Slow charge cycles just vary the termination rate (1/5c or 1/20c etc....)


Cheers