#tidytuesday posts weekly datasets for R users to explore, model, and visualize. They have an active community on Twitter. You can find the datasets here: GitHub - rfordatascience/tidytuesday: Official repo for the #tidytuesday project
Kaggle is a machine learning community that posts all sorts of datasets that you can use for your analysis. I think they also have projects/ contests.
I would recommend going over R fundamentals with the following tutorial: https://cran.r-project.org/doc/contrib/Paradis-rdebuts_en.pdf
It’s a rather short document and helped me when I was new to R. If you want to learn more about data science I would recommend R for Data Science by Hadley Wickham. It’s available for free online as a PDF or HTML doc.