Shortcuts (LibreOffice Math Accessibility)
You can control LibreOffice Math without a mouse.
Inserting a Formula Directly
If you want to insert a formula into a text document, and you already know the correct writing, you can proceed as follows:

Write the formula into your text

Select the formula

Choose the command Insert  Object  Formula.
Inserting a Formula using a Window

If you want to use the LibreOffice Math interface to edit a formula, choose the command Insert  Object  Formula without any text selected.

The cursor waits in the Commands window and you can type the formula.

You can compose formulas using the Elements pane. Open it with the menu View  Elements if it is not already open.

If the Elements pane is open, use F6 to switch from the Commands window to the Elements pane and back.