The wmsread function accesses the Internet to render and retrieve a raster map from a Web Map Service (WMS) server. The function can take input of the layer which you want to retrieve, the longitude and the latitude, and the image height and width.
It gives two ouputs. the first can be a 2D greyscale or a coloured 3D image in the format : ImgHeight x ImgWidth x RGB channel. The second output is a Geographic raster reference object which ties the image to the EPSG:4326 geographic coordinate system.
For further understanding and how to use the function, I suggest you go through the examples in Mathworks Documentation.