No worries.

If you use hive.blog, the easiest is to post from the community directly.
On the community page on the right side you have a new post button. Click it, write your post and publish it from there. It will automatically add the post in the community. It will also show in your blog.

If you use peakd.com, and you already subscribed for the community, you can choose where to post while you write a post without being in the community page.
Right above the post title you have Write a new Post. Click on it and choose the community.
As another alternative, you can also use the same method I explained for hive.blog in peakd.com too.
Go to the community page and on the right upper corner you'll see a Write a Post button. Click it, write your post and publish it from there.

Remember that after you post in Community you cannot change it. So always double check if you're posting on the right one.