Sticky Note does not have any toolbox to format the text, like making it bold or underlined, larger or smaller in size etc. So, here is a list of keyboard commands which can do so. Just highlight the text you wish to format and use the following keyboard commands:-

Bold: CTRL+B

Italic: CTRL+I

Underline: CTRL+U

Strikethrough: CTRL+T

Increase size of text: CTRL+SHIFT+>

Decrease size of text: CTRL+SHIFT+<

Bullet list: CTRL+SHIFT+L (once)

Numbered list: CTRL+SHIFT+L (twice)

Lettered list (a, b, c, etc.): CTRL+SHIFT+L (three times)

Lettered list (A, B, C, etc.): CTRL+SHIFT+L (four times)

Roman numeral list (i, ii, iii, iv, etc.): CTRL+SHIFT+L (five times)

Roman numeral list (I, II, III, IV, etc.): CTRL+SHIFT+L (six times)