There are thousands of datasets available online for practicing R programming concepts and techniques. Also, there are online competitions and challenges that include a problem statement and a dataset. You have to download the dataset and implement various algorithms using R programming to find the best possible solution to the problem. Once accomplishing that, you have to submit your solution to get it reviewed. There are thousands of enthusiasts who participate in such competitions. This is the best way to learn and practice R programming.
If you are looking for an online course to learn R programming, check out this R Programming Course by Intellipaat.