When you do machine embroidery you need a large variety of thread. As a beginner I bought thread kits. Luckily I live fairly close to Sewing Machines Plus and was able to see them in person. Here is the website:
www.sewingmachinesplus.com/thread-kits.php.
When I bought my machine I didn't realize it and just bought a few colors to get me started. When I saw the kits I was so excited. I ended up buy 3 different kits - none of them overlapped and now I just fill in when I am making something specific.