The main UK website of the Richard III Society has huge amount of information about the Life and Times of Richard III. You will also find there links to Branches and Groups in the UK and overseas which each have their own, often unique, resources.
A reading list for those new to Richard III and the Wars of the Roses is here.
There is a vast amount of information, attractively presented on the Luminarium site
If you would like to take a short, online course on the 15th century there are several choices.
FutureLearn provide free Massive Open Online Courses (MOOCs)
England in the Time of Richard III (Leicester University)
Agincourt 1415: Myth and Reality (Southampton University)
Learn to read early modern handwritten documents (University of Glasgow)
Coursera provide both free and paid courses online.
Coursera requires a lengthy registration process to obtain access to free content, just be careful not to click any box that asks for payment if you want free access.
Magic in the Middle Ages (University of Barcelona)
If you are happy to pay a fee, several Universities offer short courses.
Wars of the Roses (Oxford University)
Medieval England (Cambridge University)
Wars of the Roses (Edinburgh University)
The Workers Education Association (WEA) offer courses on a variety of topics.
The University of the Third Age (U3A) also offers courses by region