"Blir/Ble" mean "is/was" in the passive, and they emphasize the agency of the person/thing carrying out the verb. "Er/Var" is also "is/was," but the action is more generalized, and the person/thing carrying out the action has less of a focus.
Brødet er bakt hjemme. > "The bread is baked at home." The focus here is on the bread.
Brødet blir bakt hjemme. > "The bread is baked at home." The focus here shifts to the unmentioned person/thing actually doing the baking.
Brødet blir bakt av meg > "The bread is baked by me." This is the only way to translate this. If you use "av," you need to use a form of the verb "bli."