Help with using the Visual Editor is available here (opens in a new window): http://make.wordpress.org/support/user-manual/content/editors/visual-editor/
Generally we encourage simple formatting, no centering or playing with font sizes or justification.
Fun with headings
Choose your heading styles from the editor drop down when the Editor is in Visual mode, these are available ready made (in the template).
Heading 1
hello this is some para text
Heading 2
hello this is some para text
Heading 3
hello this is some para text
Heading 4
hello this is some para text
Heading 5
hello this is some para text
Heading 6
hello this is some para text
Pictures
Will make your journal come to life, but remember NOT to shrink your pictures too much.