A Dense layer in Keras is the layer that is reported to be most used inside the deep learning model. This layer is called deep as it is connected very deeply, and because of this connection receives input from each neuron present in the previous layers.
Learn yourself about Keras, from our Keras tutorial. If you are planning to get certified in these frameworks which are in use in the artificial intelligence domain, then I would recommend you to join Intellipaat’s Artificial intelligence course.
In this regard, I would suggest you watch Keras's training video.