Validation Curve Interpretation
You can understand whether your model is overfitting or underfitting  by the difference in the graph of your train and validation score. If your train score(performance not loss) is low and so is val score then your model is underfitting. On the other hand if your model is overfiiting you will have high training accuracy but your validation score will be low and the train and val graph will be far from each other. A perfect model just has high training score with the validation  curve as close as possible and the two graphs will be very close like the graph you provided.