First thing to do is to add org-page to the additional-packages portion of your .spacemacs file

(org-page :location (recipe
                      :fetcher github
                      :repo "sillykelvin/org-page"
                      :files ("*.el" "doc" "themes")))

Next add the following to the user-config portion of your .spacemacs file

(require 'org-page)
(setq op/repository-directory "/path/to/your/repo")
(setq op/site-domain "https://githubuser.github.io")
(setq op/personal-github-link "https://github.com/githubuser")
(setq op/site-main-title "TITLE")
(setq op/site-sub-title "SUBTITLE")
(setq user-full-name "YOUR NAME")  ;; not org-page specific
(setq user-mail-address "your@email.com")  ;; not org-page specific

Create your github.io page using the following directions.

Then run SPC SPC op/new-repository and specify the location you want for your repo. This should probably be the same as what you put in your .spacemacs file.

In this same location you will want to add the remote, which can be done using magit. For me the easiest way to do this is through magit-status (SPC g s) and while in magit-status type M a. From there you can just follow the prompts to add your remote.

This is as simple as SPC SPC op/new-post and following the prompts.

This should be as simple as SPC SPC op/do-publication and following the prompts, which is likely to result in you pushing y n y y.