I've been following brett manings' singing success course, but I cant reach my head voice.
I agree that falsetto is not the same as head voice, and I also know that falsetto is weak and airy.
I just want to know when I am using my head voice and some exercises for learning how to use it better

I hope you can help because my range only goes from E2 to D4, really poor isn't it?

That's why I want to lear how to use my head voice in order to achieve a wonderfull A4!!! that's my goal!

First off, as I understood, it differs by gender.

For a woman, head voice is natural if you are breathing correctly once you reach a certain note. (You might feel a slight buzzing in your sinus cavities in your cheeks.)

There may be a slight break in between your head and chest voice (called a passagio I think). Sometimes you will be able to hit these notes using your chest voice, but other times you will have to use your head voice. The key to controlling this so no one hears the break? Practice, practice, practice.....