This type of printmaking comes under the heading of relief printing. A woodblock or lino cut is made by cutting away areas of wood or lino block with special tools, a little like curved chisels. Ink is rolled over what's left of the original surface and transferred to paper using pressure.
A collagraph can be printed in the same way. However, the surface is built up like a collage by glueing materials onto a cardboard block. Many Artists like the 'rough and ready' feel of collographs, using different textures to experiment and explore how various materials take ink in different ways.