In GEM, there´s a wide variety of effects and filters that can be inserted in the GEM chain.you can find most of them in the folder /reference/Gem.(listed mostly as [pix_"something"] )
The structure of the pix effects in Gem it´s similar. we have at least one inlet and one outlet that are used to integrate the effect into the GEm chain and sometimes, additional inlets used to modify the parameters of the effect. (via message or directly with a number) Of course we can know more about the effects and his parameters by clicking into his help.
I reccommend to integrate the effect in the gem chain just before the [pix_texture]. any other effects can be added to the chain in any desired order. (each order, probably will have different result..)
Since there are many effects in GEM (this could be a new book..), It´s better to explain very clear how is the typical topology of a pix effect and anyone interested in a particular effect, can check the help for more info.