as an adjective, 'next' describes something that immediately follows the current or most recent item in a sequence.
I'll see you next week.
The next chapter in the book is very exciting.
Who's the next person in line?
as a preposition, 'next' indicates the immediate subsequent position of something in relation to another.
When 'next' is used as a preposition, it's typically followed by a noun (or pronoun) without requiring 'to' in between, although 'next to' is also a common phrase meaning 'adjacent to.'
I sat next her during the concert. (Here, 'next' implies 'next to.')
The pharmacy is next the grocery store.
She lives in the house next mine.
as an adverb, 'next' describes the subsequent action or event in a sequence.
First, preheat the oven. Next, mix the ingredients.
She finished her homework and next prepared for her presentation.
I visited Paris and next plan to visit Rome.
It's essential to differentiate between the different roles of 'next.' For instance, 'The next train' (adjective) vs. 'I live next the post office' (preposition) vs. 'What should we do next?' (adverb). 'Next' as a preposition can sometimes sound informal, and in formal writing, it might be clearer to use 'next to.'