Visual editing is part of a Labs feature in JIRA platform 7.2. Labs features can be turned off by your administrator, so if you don't have access to visual editing, that's probably why.
Administrators can enable the feature in > System > User interface > Rich text editor, or G+G search for rich text editor.
Formatting content in Visual mode gives you a What You See Is What You Get (WYSIWYG) experience. Formatting appears as you apply it, and you no longer have to flip to a Preview to see what your content will look like when saved. You still have the option to view the wiki markdown by selecting the Text tab. You'll know you have access to the visual editor because you'll see the Visual and Text tabs.
In Visual mode, you can still enter wiki markdown syntax as you add your content, and it'll be rendered exactly as it'll display when you save. You can even flip between modes to view the formatted content, and the wiki markdown syntax. You can also use the toolbar to format and style your content.
As Visual editing is really a preview of what we're working on, there's a few things that may not work quite as you'd expect them:
- Formatting content in a complex way can affect it's ability to be rendered, things like tables in the cells of other tables, and adding images to table cells won't work.
- Pasting content may not work as expected, as the source content may really be formatted using a method we don't support. So pasting tables may work, and it may not, depending on the source. Pasting plain text is absolutely fine.