Yeah, still in school (3rd year). I have intern experience, but it seems like these type of positions are way too advanced for me at the moment. Just unsure how to progress...
1. see the other comment for CMU
2. learn c++ + data structures
3. try seastar (or any other lib?) and try to follow the tutorial
4. go to mailing list and ask for help when you're stuck
5. look into issue-queue for small tasks and grow little by little
Makes sense ? Another project you may look at is https://github.com/phaistos-networks/Trinity which is a library and should be simpler than a whole framework/db (trinity is like lucene/rocksdb compared to full-db cassandra/scylladb).