Oxidation - When atoms of an reactant give away electrons.
Reduction - When atoms of an reactant assume electrons.
Electrons are charged with negative electricity. So when the atoms give away electrons they lose the negative electricity and they become more positive...
Ex: O
-2 O
0In this case the Oxygen has given away 2 electrons and has gained more positive electricity(Because now we don't have spare electrons i.e in this case the number of protons is equal to the number of electrons) thus neutralizing the first existing electricity.
Conclusion: This is oxidation
Another Ex:
Mn
+2 Mn
+7In this case the Manganese has given away 5 electrons and has gained more positive electricity.
Conclusion: This is oxidation again
When the atoms assume(receive) electrons they gain more negative electricity and they become more negative...
Ex: Cr
+6 Cr
+3In this case the Chromium has received(assumed) 3 electrons and has gained more negative electricity.
Conclusion: This is reduction
You can easily recognize oxidation and reduction.
During the oxidation the oxidation number is increasing(Don't let the negative values fool you, it is just the same, think it trough)
During the reduction the oxidation number is decreasing