Generating an hash function for unordered_map with custom Key

I need to save a set of pointers in an unordered_map, using as key a std::vector<std::vector<int>> since it's what makes my elements unique (in particular the inner vector all have the same size, and if the inner vectors are in a different order, it's still the same element).

I started looking around but having never done something like this, I got a bit lost around the various opportunities, e.g. creating a template for an hash function, calculating an unique value from those vectors and using it directly as key, hash boost library.

I'm not looking for someone to solve this problem for me, but just for someone who can direct me somewhere where I can study to figure this out. Thank you in advance!