A confidence interval is a range of values, derived from sample statistics, that is likely to contain the value of an unknown population paramete
Example:
Let's take a light bulb manufacturing factory
uses simple random sampling to select each week 50 light bulbs
to measure how many hours they burn
each week a sample mean is obtained and used as a point estimate for
true mean (mu) or the number of hours the light bulb burns
Let's assume based on historical data light bulbs assumed to have
a normal distribution with known standard deviation(sigma) of 65 hours
last week let's say 50 bulbs (n=50) are measured and sample mean that was
obtained was (x-bar = 1045 hours). so this is the point estimator for
true population mean (mu)
Interpreting Confidence Intervals(interactive visualization):
http://rpsychologist.com/d3/CI/
Confidence Interval Online Calculator:
http://www.socscistatistics.com/confidenceinterval/Default3.aspx