Consider the following balanced oxidation-reduction reaction:

Cl2 + SO2 + 2 H2O --> 2 Cl^1- + SO4^2- + 4 H^1+

Based on the above reaction:
1) Which element is oxidized ?
2) How many electrons are lost by each atom ?
3) Which element is reduced ?
4) How many electrons are gained by each atom ?

For 1 and 3. Loss of electrons is oxidation; gain of electrons is reduction.

But to do this you must know how to assign oxidation numbers to the elements on the left and right. Here is a site that shows you how to do that. Post again if you still have questions but be specific about what you don't understand.
http://www.chemteam.info/Redox/Redox-Rules.html

For 2 and 4. After you learn to do 1 and 3 you will see how to do 2 and 4.

1) To determine which element is oxidized, you need to compare the oxidation states (or oxidation numbers) of each element before and after the reaction. The element that experiences an increase in oxidation state is the one that gets oxidized.

In this reaction, chlorine (Cl) changes from an oxidation state of 0 (in its elemental form) to -1 in the chloride ion (Cl^1-). Since the oxidation state of chlorine increases, it is the element that gets oxidized.

2) To find out how many electrons are lost by each atom, you can determine the difference in the oxidation numbers of the element before and after the reaction.

In this case, chlorine goes from an oxidation state of 0 to -1, meaning it lost one electron. Therefore, each chlorine atom loses one electron.

3) To identify the element that is reduced, you need to compare the oxidation states of each element before and after the reaction. The element that experiences a decrease in oxidation state is the one that gets reduced.

In this reaction, sulfur (S) changes from an oxidation state of +4 (in sulfur dioxide, SO2) to +6 in the sulfate ion (SO4^2-). Since the oxidation state of sulfur increases, it is the element that gets reduced.

4) To determine how many electrons are gained by each atom, you can calculate the difference in the oxidation numbers of the element before and after the reaction.

In this case, sulfur goes from an oxidation state of +4 to +6, meaning it gains two electrons. Therefore, each sulfur atom gains two electrons.