You have to be logged in to create formulas. You can mark formulas as public (viewable by everyone). If not marked as public, only the creator of the formula can see it. By default, formulas are priviate.
A formula has five parts.
Sometimes, the easiest way to create a formula is to use another one as a template. When viewing a formula (either your own or someone else's) there is Clone link on the right hand side of the page.
Click on Clone and you're editing you're own copy of that formula. The copy starts with the same title and tags, as well as formula source and description. A cloned formula always starts off as private.
$\mathop {\lim }\limits_{x \to - \infty } f\left( x \right) = 1$