Vlad - OBV measures a comparrison of price and volume. On the period end, if the price is up this is added to "up volume" if down, it is added as a negative on the "down volume" side.

By looking at the ratio you can get a hint of whether the volume is higher on buying or selling. Different periods give different indications so I use it on many levels from 1 minute to daily.

Primarily, for me I look for divergences such as when price is going down but OBV is rising.