Press 6 7 8 9 after a letter (a e o u d) to add a diacritical mark to it. Press 1 2 3 4 after a letter (a ă â e ê i o ô ơ u ư y đ) to add a tone mark to it. Press the key again to type the digit 1 2 ... 9 instead. This keyboard follows the VNI standard.
Stop the mouse over each button to learn its keyboard shortcut.
Shift + click a button to insert its upper-case form. Alt + click a button to copy a single character to the clipboard.
You can select text and press Ctrl + C to copy it to your document. In your target document, press Ctrl + V, or, if you want to paste the text without formatting, try Ctrl + Shift + V.