Ionization energy is the energy required to REMOVE an electron from an atom. The trend is upwards and towards the right of the periodic table.
Think about the noble gases, they are so happy and stable. They have all the electrons they need. They do not want to remove any of them. If you try to, it will be very hard, (like taking a toy from a 2 year old). SO they would have the most ionization energy. It would take the most energy to remove an electron from them.
BUT the first column, alkali metals, are SO close to being a noble gases, all they need is to remove an electron. It would take very little energy to remove one because it is highly favored by them. That's why it would take the least amount of ionization energy.
Let me know if this is what you were looking for!