Bo vs Dlatego
When would one use bo or dlatego?
I think you mean dlatego, że
"dlatego, że", "bo", "ponieważ" mean the same but may be used in different situations, depending on personal preference and register. (all mean because -the answer to why question, the beginning of the part of the sentence that explains reason of something) ( look at discusions linked by @mixhal)
dlatego without "że" or "iż" is "so", "for that reason" "therefore"- the beginning of part of the sentence that explains result.
Dlatego is a coordinating conjunction, equivelent to the english concepts of:
therefore, so , that is why.
Bo is mostly used in expressions that are spoken ( and now also in SMS's)
Both can be possible equivalents for :
as, because, since, for.
click here for the major reference
There is also information in wiki, here that could be worth reading.
Bo and ponieważ are interchangeable. Ponieważ is a bit more formal.
Dlatego is slightly different. Together with że (in the phrase dlatego, że) it means just because, same as bo and ponieważ. However, when it stands alone, it's more like this is why.
Jem, bo jestem głodny. = I am eating because I am hungry.
Jem dlatego, że jestem głodny. = I am eating because I am hungry.
Jem, ponieważ jestem głodny. = I am eating because I am hungry.
Jestem głodny, dlatego jem. – I am hungry, that's why (or: therefore) I am eating.