'Whereas' means 'but':
'I'm right-handed whereas/while my brother is left-handed.'
'Therefore' means 'so' (we use them to express result):
'It hasn't rained for weeks. The earth is therefore dry.'
'Even though' and 'however' mean 'but':
He's fit, even though (although) he's sixty.
(even though is more emphatic than although)
'The fire destroyed much of the building. However/Nevertheless, only six people
lost their lives.'
'Besides' means 'and':
'Besides will, there are other modal verbs which express the future.'
= in additin to, apart from
'I don’t really want to go. Besides, it’s too late now.'
= it is used for making an extra comment that adds to what you have just said