TapNoiseIn many Mac editors, holding Shift while moving the insertion point extends a text selection. Add Option for word-sized movement or Command for common line and document boundaries, depending on the app.
Build a small selection first
Click inside a disposable paragraph and try Shift with the left or right arrow. Watch which characters become selected. Then try Option-Shift with an arrow to extend by words.
Line-boundary behaviour and document navigation can vary between editors. Inspect the app’s Edit menu or help if Command-based movement behaves differently from what you expect.
Check direction and focus
Selection usually grows from an anchor point. Moving back toward that point can shrink it. If a key scrolls the page instead, the text editor may not have focus; click inside the text field and retry.
On a webpage, selecting page text is different from editing a form field. A terminal also has its own line-editing controls. Do not assume every visible text area accepts the same combinations.
Replace only after a visual check
Once the desired passage is selected, pause briefly before typing. New text normally replaces the selection. That makes a selection mistake more consequential than a navigation mistake.
Use Undo immediately if the replacement is wrong, and verify the restored text. For correcting a single word without selecting a passage, word deletion may take fewer steps.
Source: Apple’s text and document shortcuts.