How to charge 18650 lithium ion cells together?
What charger voltage?
Do you really mean laptop power supply?
ie the often 19v rated supplies are NOT a charger by themselves - the charger proper is inside the laptop. 

6S = 6 cells in series.  3S = 3 cells in series. 2P = 2 strings in parallel.
3S2P = 2 strings in parallel. Each string = 3S.  

Minimum final charge voltage for 6s LiIon = 4.2 x 6 = 25.2V so average 19V psu will not work. 

3S2P = 3 x 4.2 = 12.6V so you need a buck converter or similar from 19V.
Even a psu of the "correct" final voltage is just waiting to destroy cells if used by itself.  

What you need is a dedicated LiIon charger. You can design and build these from parts but in most cases buying a 3S2P commercial charger is easiest and lowest cost. Max current for 18650 is USUALLY in the 1A to 3A range. You need a datasheet for the cells to see what Imax is safe.  While SOME cells allow C/1 rate charging and have 3000 mAh capacity so 3A is OK, others allow only C/2 charging and some MAY have capacities closer to 2000 mAh so only 1A max may be allowed. Anything much over 3000 mAh is a fake.
Even the highly reputable Panasonic only allow C/2 max for some of their LiIon cells.