Formatting is never fully automatic. You always instruct Writer in some way for bold, italics, font changes, colour, …
You can use the toolbar button for that or their keyboard shortcuts. This is generally good for experimenting and have a quick feedback for the stylistic variation with regard to font face. But this direct formatting (in LO parlance) creates a formatting nightmare.
Documents are never perfect from the start. Formatting is a visual art and needs heavy improvement before the final copy is ready.
If you use direct formatting, every sequence is unique and must be separately reviewed and modified.
A high-valued featured in Writer is styles. Styles are more elaborate than in many other office suite (notably M$ Word) because they address not only paragraph, but also character (for intra paragraph “enhancements”), pages, frames (for inserted pictures or illustrations) and other more specialised uses.
A style describes the properties of it target (paragraph: alignment, spacing above and below, indents = additional left and right margins, font, language, …; paragraph: font – face, size, weight, angle, colour … --, language, position, …; page: margins, header, footer, numbering, …).
A style is applied to paragraph, sequence of characters, … to “type” the target. When a style is modified, the change applies instantly to all targets “typed” with the style. Compare to the situation where you must change all paragraphs one by one.
Styles are described in chapters 8 and 9 of the Writer Guide. But start by experimenting on a dummy document to get accustomed to the workflow.
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