Hi.
Welcome on Gothicat World.
If you don't want or cant buy jewels, you can find some by sending your creatures in exploration, which you can do by going on your creature and click on the image above "Explore", just here:
But they are rare to find, so except if you're really lucky, you won't find jewels in exploration by only sending 5 creatures per day.
Otherwise, you can find jewels by playing Gothi-lucky, which is a game appearing sometimes in the year for events. (the last one was the Video Games Day)
And if I'm not forgetting something, this is it.
Hope I helped you. ^^
Have great Holidays (and sorry for my english)