Learner dictionaries are specially designed for language learners (and teachers), and are usually much more useful than general dictionaries.

They contain far more information than simply the definition(s) of words: audio for pronunciation, information about British and American English, style/register, collocations, grammar and patterns, and so on.

Cambridge: https://dictionary.cambridge.org/dictionary/english/

Cambridge: https://dictionary.cambridge.org/dictionary/learner-english/
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Oxford: www.oxfordlearnersdictionaries.com

Macmillan: www.macmillandictionary.com

Longman: www.ldoceonline.com

Collins: www.collinsdictionary.com/dictionary/english

There is also a grammar section in the Cambridge dictionary.
Cambridge Dictionary grammar pages: https://dictionary.cambridge.org/grammar/british-grammar/​