1. How can a RANDOM sample be selected?
There are lots of ways ranging from picking names out of a hat to using computers.
On a computer, most spreadsheets have a RAND(..) function and most calculators have a RND# button
2. What is the difference between a sample and a population?
A population covers all of the group being studied.
A sample is part of that group.
The larger the sample, the more likely the sample is to be representative to a population.
3. Why should a sample be random ?
If a sample is not RANDOM it is likely to lead to BIASED results.