There exist multiple good, free encyclopedias of philosophy online:
https://plato.stanford.edu/entries/life-meaning/#Nihi
https://www.rep.routledge.com/articles/thematic/nihilism/v-1
Stanford's is probably the best-regarded of the bunch—you'll struggle to find a better brief introduction to most topics, than it provides, especially for $0. Skipping e.g. Wikipedia and going straight to the SEP, for philosophical topics, is usually a good call.