Click on the hero whose glyphs you want to enchant.
Click on Glyphs on the side menu.
Click on the "To Forge" button.
Select the glyph you want to enchant. Click here for a list of the best order to enchant glyphs for specific heroes.
Click on the different runes to fill up the level bar. You should use a combination of smaller runes and larger runes. When you're done, click the "Enchant" button.