A life policy is a contract: you pay premiums, and when you die the carrier pays the death benefit to your beneficiaries. The benefit is a fixed amount named on the policy, paid directly to the people you name without passing through probate, and generally not counted as income to them. What the policy is for decides how large it should be and how long it should last: replacing a salary until the children are independent, paying off a mortgage, funding a business buyout, covering estate taxes, or simply paying for a funeral.
There are two families of policy. Term life covers a set number of years at a level premium, pays only if you die in that period, and builds no value; it is the least expensive way to buy a large benefit for the years a household depends on an income. Permanent life, which includes whole life and indexed universal life, is designed to stay in force for your whole life, costs several times as much for the same benefit, and accumulates cash value that can be borrowed or withdrawn.
The premium is set by underwriting: your age, sex, health history, tobacco use, family history, driving record, occupation and hobbies, the amount and term chosen, and the carrier's own pricing. Two carriers can put the same applicant in different rate classes, so a life application is worth shopping across several carriers before it is submitted, because an application that draws a poor class becomes part of the record.
The analysis starts with what the benefit has to do, arrives at an amount and a duration, and prices the policy type that fits across the carriers we represent. If the group coverage at work and the savings you already have cover the need, that is what you are told.