The MC software comes with two specific but different 'login' pages. One is within the site design, with top/left/right/bottom navigation areas and is used mainly by sites that allow customers without a login to browse first. The other is a more lean login page, with an optional header/footer and just the login form. The latter is used more often by sites that disallow public viewing of their products and request or require login first.
To help you find either link, or to add one to your site you can have the MC software automatically display a login link within the Horizontal Navigation Bar, by going to Site Information > Site Wide Settings > General Storefront > Hide Horizontal Navigation Log In Link and set this to 'No'. Make sure that the setting above that for Display Horizontal Navigation Bar is set to Yes.
To change this link from one option to the other, go from the above menu to Site Information > Site Wide Settings > Log In & Checkout > Display Log In Page within Storefront Center Content Area. If you set this to 'Yes' you with get the page with the site navigation around it. If you set it to 'No' it will be the leaner option.
If you are coding these manually in your own HTML, you can use -
CODE
<a href="index.asp?PageAction=LOGIN">Log In</a>
- for the INTERNAL page and -
CODE
<a href="login.asp">Log In</a>
- for the more external one.
One note of interest, both pages are available at the same time, and if you have a need to, you can link to them each separately and they will perform the same function. The setting within 'Log In & Checkout' mentioned above merely switches the link on the Horizontal Navigation Bar.