There are two ways you can add a post to the platforms via Hootsuite.
1. Quick Post - This allows you to post to more than one media platform at a time, although it is restricted by the lowest account functions.
Selecting the drop arrow on the quick compose allows you to have a selection pre selected or select each time you quick post.
Having selected what platforms you want to post out to, the display will show you how many characters you are restricted too.
You can attach images, files, and also schedule these posts for a future time.
2. Specific Posts - Using the actual feed columns to post to each specific platform.
Using the WordPress example, you can post to a similar level of control as you can through the site. You will need to ensure you select visual on the post, this will allow you to write and attach images without using any display code.
Once you have created a new WordPress post, you can then share this with all the other platforms by the share facility.
You can then select which other media forms you want to publish this to.