How to define confusion matrix for classification?
You are just predicting if Play = Yes or Play = No.

The confusion matrix would look like this:

             Predicted
          +------+------+
          |  Yes |  No  |
    +-------------------+
A   |     |      |      |
c   | Yes |  TP  |  FP  |
t   |     |      |      |
u   +-------------------+
a   |     |      |      |
l   | No  |  FN  |  TN  |
    |     |      |      |
    +-----+------+------+

TP: True positives
FP: False positives 
FN: False negatives 
TN: True negatives


The accuracy can then be calculated as (TP + TN)/(TP + FP + TN + FN).