People put their pronouns so you know how to address them correctly. It prevents confusion for people addressing trans-/bi-gender people or gender fluids or non-binaries, etc.
Bigender = Two genders
Transgender = Gender opposite to sex
Gender fluid = Gender changes every so often
Non-Binary = Not entirely male or female
Agender = Neither male or female (gender neutral)
There are a lot more. I'd advise you'd learn the basics, to avoid offence and ignorance.
Comments on Profile Post by NevePlaysDota