Kernel is the parameter convolution layer used to convolve the image. The convolution operation is shown in the following figure:
The kernel has two parameters, called stride and size. The size can be any dimension of a rectangle. Stride is the number of pixels moved every time.
A stride of length 1 produces an image of almost the same size, and a stride of length 2 produces half the size. Padding the image will help in achieving the same size of the input.