Do you mean

• JavaScript, the widely used scripting language that is built into the browser
• the Java plugin, no longer used in Firefox or Chrome

To confirm that JavaScript is enabled:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste javas and pause while the list is filtered

(3) If the javascript.enabled preference is bolded and "modified" or "user set" to false, double-click it to restore the default value of true

The "Tools" menu is on the classic menu bar. You can activate it temporarily by tapping the Alt key or pressing the F10 function key. However, there's nothing on there about JavaScript (or Java) as far as I can remember. Possibly the instructions you were given are very old now...

P.S. If you need to use the Java plugin, try Internet Explorer.