Does the LastPass icon (asterisk in a box) appear in your browser's toolbar? If it does, is the background gray or red? If gray, click on the icon and log in.https://lastpass.com/support.php?cmd=ge ... feataure_0
has a series of articles that may help.
Normally, LastPass will offer to save information when you log in to a site. It may be that the browser extension isn't enabled, in which case the first article in the link above should help.