What is the diffrence between oxy and hydro

Assuming you are referring to oxycodone and hydrocodone:

Both are semi-synthetic opioids. Both are used in different combinations to relieve pain. Hydrocodone is used as an antitussive (to relieve cough). Oxycodone is not.

Each contains a constituent derived from the opium poppy albeit from different components.

Each is metabolized by different enzyme systems resulting in different metabolites, hydromorphone and oxymorphone, although each being identifiable via the crossover commonality of morphine.

Your question would allow for responses ad infinitum. If you can particularize your question... can probably be of more assistance. For instance, are you interested in medical usage, abuse potential, pharmacokinetics, pharmacodynamics, etc.

The general usages and characteristics of the subject drugs may be obtained by clicking on the respective sites noted below:

NIH >Hydrocodone (http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000014/)
NIH >Oxycodone (http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000589/)