just doing a fast tutorial to help someone

1.First please click on your observatory 

as you can see this building holds all your sketches

this is only a viewing area.. you can not discover them there

you have to go into the discoveries which im getting to that area

2.Moving over to your Discovery tab 

3. once tab is open you have a wide selection of all your sketches

here you can mouse over any area, 

shows you sketches you have and don't have, and doubles you may have just mouse over the image to see

Hope this helps in how to manage your discoveries/sketches