Self-esteem is how much you value yourself as a whole; confidence is how sure you are that you can do a particular thing. The first is an attitude towards yourself, the second a belief about a task, and people can be high in one and low in the other.
Two different questions
The Rosenberg Self-Esteem Scale asks ten questions about worth and satisfaction, such as On the whole, I am satisfied with myself and I feel I do not have much to be proud of (Rosenberg, 1965). None of them names a skill. The nearest is I am able to do things as well as most other people, and that is a general comparison, not a judgement of any ability.
The research word for confidence is self-efficacy, which Bandura (1977) defined as the belief that you can carry out the behaviour a situation calls for. In his account it is specific: confidence about public speaking says little about confidence in arithmetic, and it is built mostly from past success at the task itself. A confident surgeon can be an unconfident parent, and neither fact tells you how she values herself.
Where they overlap
When confidence is measured as a general trait rather than about a task, the two stop looking different. Judge and others (2002) found that measures of self-esteem, generalised self-efficacy, emotional stability and locus of control were so strongly related that they behaved as indicators of a single core evaluation of oneself. A person who believes they can generally cope and a person who feels they are generally worth something are usually the same person.
What a self-esteem score does not mean
A high Rosenberg score does not mean you will feel sure of yourself in an interview or an exam; those are self-efficacy questions, and the scale does not ask them. A low score does not mean you lack skill, and people who are good at what they do can still feel they do not have much to be proud of. The score is not a diagnosis of anything, and it is not a prediction of how you will perform.
What it means for your results
Read your score as an answer to one question: on the whole, how do you feel about yourself? If you came to the test wondering whether you are good at something, the scale cannot tell you, and the site has no test that can; confidence in a task is best read from your record at that task. If you came wondering why you doubt your worth despite being capable, the answer is in the distinction: the two are different things, and the scale measures only the first.
The self-esteem test takes two minutes and is scored on your device, with your score drawn on a strip against the possible range of 10 to 40.