Need Help - search form with multiple dropdown

[eluser]mariuskmc[/eluser]
Greeting
I stumbled and hope someone can help me.

I need to do a search form with jquery for the following structure:

Category - dopdown
Country-(Country of Category) - dropdown
Oas - (city in the country and category) - Dropdown
Offer Name - Form input
Submit

I tried all the existing documentation ... But I did not create a functional variant.

It may help me with an example

sorry for my English