How to setup fluval u4 oxygen

[Ramase]

Hello all

I have a fluval u4, I'm told it can be used to add aerarion, it has a valve at the top and 2 opening on the outside

It is submered fully under water but I'm unsure how i setup the added aeration?

I have a wave maker set just below the top of the water breaking it up but if possible would like to utilise the aeration/oxygen from the u4

 

[Essjay]

The bit outlined in red (the top of the venturi valve) needs to be out of the water or it can't suck air in. Looking at your photo, the blue cap seems to be missing - that controls the amount of air being sucked in.
The diagram in the manual shows the filter positioned so that the top of the filter breaks the surface.