The British Council has this nice website for ESOL learners
https://esol.britishcouncil.org/
A Website for Studying English as a Second Language
http://www.manythings.org/
YourDictionary is the easiest-to-use online dictionary. It is a dictionary you can understand with lots of tools to help you choose your words precisely, understand a word, avoid usage pitfalls and be confident in your use of words.
https://www.yourdictionary.com/
Common Errors in English Usage
https://brians.wsu.edu/common-errors/
Vocabulary.com has a number of lists, plus information about roots and suffixes
https://www.vocabulary.com/lists/