First of all you are not going to find the answer in a book!
Nobody own's feminism or has copyright on it.
It will be down to you.
Do you feel you are disadvantage by being a woman in whatever part of society you live in?
If yes, and you think it is unfair that you are, then you are a feminist.
But as mentioned up thread it is far more complicated than that, because having recognised that what would make the world (men) change so you did not experience disadvantage?
It could be said that "feminism" it accepting the world as men have made it, but that somehow allowances should be made to that women can function equally in that world.
Or if you believe in women's liberation than you dont aspire to be like men, but know that men as a sex class oppress women as a sex class so that in fighting for women's rights you are also attacking or wanting men to lose their privilege.
And this is without even getting onto the basic problem for women that is male violence.
Men are afraid that women will laugh at them. Women are afraid that men will kill them. Margaret Atwood.
This illustrates the profound difference for women living in a male dominated world.