Pick a type on the top, pick a type on the side. Find the point where they meet and there you go. For example the point where Dragon top, Ice side, is a green box which means normal effectiveness, while Dragon side, Ice top, is a blue box which means super effective.
I laugh as I watch people ignore the past, lie about the present, and misrepresent the future.
If a pokemon has 2 types, you have to combine the outcome. For example, Ludicolo is Water/Grass. A Fire attack is not very effective against Water, but super effective against Grass. The outcome is a neutral hit that deals neither increased nor reduced damage. A Water attack would be resisted by both types, so it ends dealing 1/2 * 1/2 = 1/4 the damage.
It says right there on the chart. For the attacking type, look at the top of the chart. Then find the defending type on the left side. Where they intersect shows the attacking types effectiveness on the defending type.
For example, say Dragonite uses Outrage on Clefable. In order to find what happens, locate Dragon on the top of the chart, then find Fairy on the left side. Where they intersect is the symbol for "no effect," so Outrage has no effect on Clefable (Dragon has no effect on Fairy).
Official Rinzler of the Kingdom Hearts III Board R - Hyuck hyuck hyuck!