Adding the WishList Member (Login) widget to a site is a relatively quick process.
This can be done in the Appearance > Widgets section in WordPress.
You should see the WishList Member widget in the list of available widgets. You can just drag that widget to the sidebar on the right (like any other widget) and it will add the widget to your sidebar.
This places a login form into the widget area of the site.
The widget itself follows the same styling as your other sidebar elements so if you would like to customize the styling in any way, you can check out the Advanced Options > CSS section of WishList Member.