I have performed topic modeling using LDA and NMF. I have also built an article recommendation engine using TF-IDF where by giving a keyword, the engine would suggest the top most documents by using cosine similarity from the pool of documents.
Below are the few blogs I have followed to complete this project and gained good knowledge on topic modeling using Gensim.
https://towardsdatascience.com/topic-modelling-in-python-with-nltk-and-gensim-4ef03213cd21
https://www.machinelearningplus.com/nlp/topic-modeling-gensim-python/
https://towardsdatascience.com/topic-modeling-and-latent-dirichlet-allocation-in-python-9bf156893c24