How to use stock from tablet
It depends on the kind of stock cube. Drier, powdery stock cubes can be crushed and sprinkled in and the appropriate amount of liquid added. 

Paste cubes should be broken up (I often chop them with my knife so as not to get sticky stock paste on my fingers) and placed in hot water before adding to the dish, because they don't dissolve as readily as the powdery cubes.