The difference between BO and PONIEWAŻ is the same like between 'CAUSE and BECAUSE. Word "bo" is shorter version of "ponieważ" but remember... Ponieważ sounds more polite and can be use in formal conversation. Bo is rather informal and use it talking to you friends in daily life. DLATEGO means THEREFORE. It is used to explain your thought. But if you want to use this word instead of "ponieważ" you may use it adding ”że”. Say "dlatego że".