The flower on my Calla lily has gone and now there are these seeds where the flower was. I was wondering if the seeds were able to be planted. How long would they take to start growing? Is there anything special they can be used for? Anything on them would be nice.
A guess at the name of the plant you might mean has been made above as a comment with a link to an image showing Calla palustris, and you have confirmed that's your plant.
However, there is a great deal of confusion caused by the use of the common names 'calla' or 'arum' for another plant called Zantedeschia - there are plants called Calla palustris and Arum (maculatum, italicum) which are unrelated, though they have vaguely similar flowers. Since you describe your plant as having white marks on the leaves, it won't be Calla palustris, because it does not have white marks on the leaves, so it must be either Zantedeschia or Arum. Image of Zantedeschia variety here
Since its not entirely clear yet which plant you have, I'll just provide the link below which gives instructions regarding harvesting the seeds (note it refers to calla lilies, yet it means Zantedeschia) rather than quoting what it says
If you save and sow the seeds and they grow, it will be a minimum of three years before the new plants flower. You can, though, split Zantedeschia plants if you want to increase your stock more quickly. There is also a plethora of videos on youtube showing how to collect Zantedeschia seed.
If, though, the plant you have with white marks on the leaves has produced a short stem covered in green 'berries' which are turning red, then its not Zantedeschia or Calla palustris - its Arum, and those seeds are toxic.
Note: just as a point of interest, there is so much confusion about the name Calla, I found an SF Gate link regarding collecting seeds from Zantedeschia, naming the plant correctly at the top, though also using the common name calla thereafter, but the picture they have with the link is clearly Calla palustris, not Zantedeschia... information on the internet becomes less and less reliable.
Its probably a lot easier to give a clear, simple answer if you add a photo of your plant.