Differentiate between Correcting spelling errors & Thesaurus?

A Thesaurus gives different Words of similar meaning.

A Dictionary gives all the Words in a given language, together with their correct spelling and meaning.

Neither tome gives any aid in grammar, which includes punctuation and syntax. That has to be learnt by practice.

'Grammar', means 'Greek teaching' as the Classical Greeks were the first civilisation to structure the language into nouns, verbs, adjectives, adverbs, sentencesetc.,

'Syntax' is the putting together the Words in th correct order, in order to convey the author's meaning.