Let me give you details explanation for Model validation Technique for Logistic regression :
Why do we require model validation ?
Ans : Model validation is essential to identify whether the model which we have made is good or not . Also how well does the model fit the data .Which predictor are most important, and how accurate is our model.
To identify whether the logistic regression model is good or not : we can use likelihood ratio test or
Pseudo R^2 or Hosmer-lemeshow test etc
Now to check how accurate our model is : we can use Confusion Matrix, ROC,
(i.e. you can say its a performance check method)
To check for variable importance we can use function varImp which is present in caret package .
For validation of model : we can use K-fold cross validation technique to check whether the model perform well on different data set or not.