Erwin Schrodinger came up with the cat thought experiment as a way of illustrating what he saw as absurdities in trying to apply the Copenhagen Interpretation to the everyday world. The Copenhagen Interpretation was a particular interpretation of quantum physics (no need to go into the details of it here).
As for something being in 2 places at once, that is just how QT represents things; it doesn't necessarily mean something actually is in 2 places at once. It's concerned with what happens up to the point of obversation. QT says there is no way of knowing the state of something until it is observed or measured. All possible states must be considered with varying degrees of probability.
In the case of Schrodinger's cat there are 2 possible states, each with equal probability. As there is no way of knowing the condition of the cat before the box is opened it must be taken as a 50% probability that the cat is alive and 50% that it is dead.
HERE is an interesting little snippet.