'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

Actually I think an online dictionary with the translation of your first language just can perfectly help you out. Watch the property of the word after you get the basic meanings.