The default text editor tool called Tinymce, it provides two views to edit your post, Visual view and Text view.

Visual view give you couple of editor tool icons, you can use these icons to edit your post just like use Microsoft Word.

Notice: The last icon is a toolbar toggle, click it will give you more editor tools.
Tips: Enter key will create a new paragraph, if you just need a new line, use Shift + Enter.

When you need copy and paste some content to your post, you can use Paste as Text tool to paste the content, this tool will remove all original formats, then you can format the content by yourself, this may let you content neat and clean. If you paste directly, it will keep the original formats.

Text view can be used for editing text in html model, it give you couple of html tags, so if you familiar html language, you can use these tags to build you content.