This link will take you to the blogs page:
https://www.pokecommunity.com/blog.php
On the left you should see "Post to your blog", click that and you should be able to figure it out from there.
Though to be honest I wouldn't really recommend bothering with blogs on PC, they've not been very visible or accessible for years and that's intentional, and I'm like 90% certain it's going to get the axe when PC undergoes its major update sometime this year.