The phrase "complete amateur" means someone who has little or no experience or skill in a particular activity or subject. They are a complete beginner and may lack expertise or knowledge in that area. Full definition
But I've been getting to play around with Tilt Brush this weekend, and as we've noted before, it's a lot of fun even for complete amateurs. (theverge.com)
Try racing against literally hundreds of cars, all driven by complete amateurs and none of which cost more than 500 bucks. (wtf1.com)
I'm a complete amateur at photography so I'm not exactly surprised with the results. (marisamoore.com)