The Mix Texture node is used for mixing two textures together. In Figure 1, a Marble Texture is combined with a Checks Texture using the Mix Texture connected to the diffuse component of an Octane material. The Amount slider is used to balance the strength of the two textures.
Figure 1: A mix texture is used to combine a Marble texture and a Checks texture. The result is connected to the Diffuse channel of an Octane material.