The first step is to find six different square numbers that sum to 196. 
For example, 1 + 4 + 25 + 36 + 49 + 81 = 196; 1 + 4 + 9 + 25 + 36 + 121 = 196; 1 + 9 + 16 + 25 + 64 + 81 = 196. 
The rest calls for individual judgment and ingenuity, and no definite rules can be given for procedure. 
The annexed diagrams will show solutions for the first two cases stated. 
Of course the three pieces marked A and those marked B will fit together and form a square in each case. 
The assembling of the parts may be slightly varied, and the reader may be interested in finding a solution for the third set of squares I have given.