ok its very simple,
1. go into the gallery section and start a new topic
2. tell about your build and give a detailed description
3. once your done giving a description click additional options
4. browse for a screenshot you took of the build in Blockland\screenshots (if you havent go in game and press ctr+p) and open it
5. then hit the other browse button and go to Blockland\base\saves and open the savename.bls (savename being the actual save name)
6. your done