In survey research, the people who respond to the survey are a sample of the population. The goal is to obtain a representative sample to be certain that the people who respond to the survey represent the thinking of the entire population, as if you had a 100% response rate.
Confidence level tells you how confident or certain you can be that your data is representative of the entire population. Most researchers strive for a 95% confidence level, meaning that you can be 95% certain that the results reflect the opinions of the entire population. However, some studies require higher confidence levels of 98%, 99%, or 99.9%.
Sampling error is the probability that the responses do not reflect the opinions of the entire population. For valid data, sample errors are typically 5%, 3%, or 1%.