From what I believe in, soulmates and twinflames are similar but super different.
Twinflames are what the media and peopl reffer to as soulmates, a person that is "made for you". There are several ways to explain them, but basically when our soul started its journy many time ago, it was made of two halves, which were separeted and born into different people, many people see them as kind of a divine femenine and masculine type of thing.
You will have A LOT of similarities with your twinflame, but at the same time you will be very different. You may notice that both of you went throught very very similar experiences on key parts of your lives, but that they affected each of you on a diferent way.
So, they are on a way your "other half" and they are meant to help you on your journey, but in order to meet each other, both of you have to have the need to change, or else it is less likely, and if you do meet, the relationship (which can be platonic or romatic btw) will be very rocky, since the main goal is to work on yourself.
As for soulmates, they are people that you met on a past life, people you had a strong bond with. Some of them are just meant to come to your life, teach you a lesson and then leave, thats why not all soulmates relationships are going to be possitive, romantic or like pulled out of a princess tale.