what is the difference between oglądać and oglądnąć?
oglądnąć is not proper Polish (can be considered slang) - but it is formed regularly - many perfective (dokonany) forms are formed by adding a -nąć suffix to the root of the verb (rąbnąć, palnąć, krzyknąć, klepnąć) - (the proper perfective form of oglądać is obejrzeć - different root here - like in the case of brać-wziąć)
-nąć suffix does not always indicate perfective aspect though - as in the case of biegać- biegnąć (similarly pływać-płynąć) - biegać is a frequentative of biec (or biegnąć) (frequentative means that the action is repeated) - biegnąć (or biec) means to be running - on biegnie - he is running - on dużo biega - he runs a lot (repeated action)