'But' is a conjunction used to address a contradictory statement or used to contrast two opposing ideas. 'But' is a cooperative conjunction. Subordinate conjunctions that mean the same thing as but are: 'although, even though, whereas, & while'. 'However' is a transition word that has the same meaning as but.
'Therefore' is a subordinate conjunction that shows result. A similar subordinate conjunction showing result would be 'thus'. A coordinating conjunction that means the same as therefore would be 'so'
'And' is a coordinating conjunction that gives additional information. Synonyms would be 'also' and 'in addition'
'Then' is an adverb of sequence that is used at the beginning of a sentence that shows the next step in a process.
