Hi Jesjes, I don't know what a sausage tree is, but the way flowering plants work is -
1) Produce flower which has pollen and usually ovaries.
2) Either - attract insect or other moving animal to take pollen to another flower, preferably on another plant of the same kind
or - spread lots of pollen on the breeze hoping it will find a suitable ovary on another plant of the same kind.
3) Pollen arrives at ovary and fertilizes it
4) Seed develops - often in some sort of carrier, like a seed pod (which is what your "sausages" are) or in other ways, like a blackberry which is a cluster of seeds in a juicy casing. The seed can be on the remains of the flower - think of a daisy - or behind it, like an apple. And I'm sure you could think of other arrangements.

So the seeds are in the pod, but the pod's only there because the flower was fertilized.