Oxides can be acidic or basic or neutral on the basis of their tendency to make acids or bases in a solution.
Acidic oxide like CO2 forms H2CO3 (carbonic acid) when dissolved in water.
CO2(g)+H2O(l)→H2CO3(aq)
Basic oxide like Na2O forms NaOH (sodium hydroxide) when dissolved in water.
Na2O(s)+H2O(l)→2NaOH(aq)
Neutral oxides do not lead to either acidic or basic solutions. Their solutions are neutral. Example - CO,N2O etc.