As Marko says you have to charge the cells in series with a CC/CV charger. This charger first pumps CC (constant current) into the battery until its voltage reaches 4.2V per cell, then it switches to CV (constant voltage) to finish topping up the charge. End of charge is detected when the current drawn by the pack goes lower than a threshold. You'll also need a safety timer.
You need to ensure the batteries' specifications are met: maximum charging current they can take, end of charge voltage, acceptable temperature range for charging, etc. Read the docs.
And, also very important, the cells need to be balanced. One of the cells will inevitably have lower capacity than the others, so when charging it will reach its max voltage first. At this point, the other cells are not fully charged, but letting the CC phase go on will result in overcharging the lowest capacity cell, which can shorten its life or start a fire. Thus, you need a balancing circuit, which will detect and prevent this. This is usually done by placing a shunt element across each cell, in order to shunt away the full charging current from the cell that has already reached maximum voltage, while still charging the other cells.
There is no way to know if the BMS you link implements this feature, so I cannot tell if it will do what you want. It does seem to monitor the voltage on each cell, but this may only be to prevent over-discharge of the lowest capacity cell.
Since Li batteries are expensive and can be dangerous, buying a $2 BMS without docs is maybe not the best idea. I'd recommend paying more for something that has documentation so you know it'll be safe.