Press Alt with the appropriate letter. For example, to type ⊂, ⊄ or ⊆, hold Alt and press C one, two or three times.
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.
After pasting, you may need to choose the right font in your target application to see all the symbols. On Windows, try Cambria or Lucida Sans Unicode.
This online mathematical keyboard is limited to what can be achieved with Unicode characters. This means, for example, that you cannot put one symbol over another. While this is a serious limitation, multi-level formulas are not always needed and even when they are needed, proper math symbols still look better than improvised ASCII approximations.
∀(x, y ∈ A ∪ B; x ≠ y) x² − y² ≥ 0
For all (x, y :- A u B; x != y) x^2 - y^2 >= 0
The advantage of using plain Unicode is that you can copy & paste your text into any text file, e-mail message or HTML document and it will (usually) be displayed correctly without any special plugins. If you need to type more complex mathematical formulas (e.g. fractions), you should use LaTeX or MathJax.