Clearly it's a suction feed single action.
My recommendation is get rid and buy a cheap double action ab and mini compressor set from ebay, (about £60).
A da is much more controllable.
However, to persevere, check the following.
Air coming out of the top pipe blowing forward.
The upright nozzle must be screwed down so that, (looking from the side), the flat tip is inline with or below the air output hole. If it is above the air cannot pass the top creating an area of low pressure and therefore a vacuum which draws the paint up the emulsion tube.
Check all seals are present, jar to brush, hose to brush and propellant etc
Check the emulsion tube and nozzle are clear.
Check it's not fouling the bottom of the paint jar.
Check that the paint is thinned appropriately, it needs to be a milky consistency, so it sticks to the side of the jar if swirled but only a thin coat, you shouldn't need much air to get the paint to flow.
If the above are ok it should work.
I know some or most have been mentioned in previous replies but having started with a sa brush myself was hoping to get everything step by step for you. I may do a quick video with my old badger sa for youtube to cover this as a few have asked on here.