The process is easy! First find your Academy's Course listings page, by hovering over Training and clicking Courses. On this page, search for the course you want to enroll in.
When you find it just click the course's title, and the course's About page will open.
To enroll in the course, just click on the blue Enroll button on the left side of the page.
You will then be led through the course. Please note that some courses have their lectures set up to be taken in order, some do not. You can verify this by checking the course's order on the top right of the screen.
Read more: How can I navigate the Course listings page?