test_size

This parameter decides the size of the data that has to be split as the test dataset. This is given as a fraction. For example, if you pass 0.5 as the value, the dataset will be split 50% as the test dataset. If you’re specifying this parameter, you can ignore the next parameter.

Here is what the above code is Doing:
1. We are creating a DecisionTreeClassifier object.
2. We are training our classifier on our training data.
3. We are making predictions on our test data.
4. We are calculating the accuracy of our predictions.