In Exposure 4, there are a number of settings that incorporate textures into the effect. For example, in the Lo-Fi category there are light leaks, many vintage settings have dust & scratches added, and old borders.
If you would like to change the texture for a particular setting you can do so by going to the "Age" tab on the right. We have provided a number of texture presets in the "Texture" groupbox. Each category has a number of variations of that type of texture.
Press the random seed a few times if you want to flip or rotate the texture. Note, a few textures (e.g. the light leaks ones) are constrained so you can't rotate them.
If the texture is too strong then you can tone it down in the middle with Protect Center or everywhere with Opacity.