Womyn is a word made up to describe women who want to be seen as equal to men. Sometimes people spell women this way to show that they want to be recognized as their own group, with their own ideas and experiences.
It's like when you and your friends have different toys and games that you like to play with. You have your own group and you want to be recognized for the things that make your group special. Womyn feel the same way about being recognized as a group that has its own unique experiences and perspectives.
Just like all people, womyn want to be treated with respect and fairness. So, some people use this word to show that they support the rights of women and that they believe in equality for all people regardless of gender.