1S 3.7v 18650 battery protection board.  This board is used for lithium ion battery 18650 model. 
This board protect the battery from over charge protection, Low discharge protection.
This BMS board is for 1S 5A Current. 
Remember 5A curent does not mean 5AH. 5A means for max 20 watts motor. You can make the battery pack even 100AH but the output power shuld be limited to 20 watts max if you want to use this bms baord.