This keyboard attempts to help you to type any letters used in Nigerian orthographies.
On desktop type the key closest to the symbol you want (a for ə or a̠, e for ɛ or ẹ etc) and then type the semicolon key. Keep typing semicolon to switch between different symbols. After typing the base letter if you want a diacritic (tone mark or nasal) above the letter then type the top left 'back tick' key. For a nasal hold down shift as you type this.
On touch devices, press and hold down a key to see alternatives. For diacritics press and hold on the 'q' key at the top left.