Press Alt with the appropriate letter. For example, to type ŵ, ẅ, ẃ or ẁ, hold Alt and press W one, two, three or four times. Alternatively, press Alt + 1 2 3 4 after a letter to add a diacritical mark to it.
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.