I've got the login control on a separate tab/page. I want to change the look of the control. How would I go about doing that? I'm new to this DNN.

What part of it do you wish to restyle - is it the skin design for the actual page that contains the login control or the styling of the login module itself?

If it is the login module itself you will need to use techniques similar to these tutorials:
Troubleshooting DotNetNuke Skins

How to style and skin the search box in DotNetNuke

Yes, it is the module itself. Thank you.

You will need to use the techniques outlined in: Troubleshooting DotNetNuke Skins to identify the IDs of the login controls and then you can style them using CSS in your skin.css file.

eg. for styling the login button:

.StandardButton {
background-color: green;
color: #fff;
font-weight: bold;
}