'learning_curve function and its arguments

I recently started to learn Machine learning.

I am trying to understand learning_curve function from sklearn.

learning_curve(model, X_train,y_train, train_sizes, cv = 5)

What I don't understand is why am I using the training data set?

I have watched so many videos and some use a whole dataset eg. X, Y or features and labels. And some use train datasets eg. X_train and y_train.

I feel like I need to use either a test or validation dataset to see how well it is learning.

Can someone clarify this for me, please?

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