witch kind of app i can build on Bubble?
Here are some good examples: https://bubble.io/showcase
Check out the very same question on Bubble’s FAQ page (about half way down)
In terms of what you can build, there is a lot of scope from simple to very complex/advanced apps. Also see the templates available and you see replicated sites like Fiverr, AirBnb and so on…
Some things Bubble are well suited and other things maybe not - it really depends on the app you wish to build and the scalability you forecast.