The organizing theme of a life table is that a cohort is tracked until the last one dies. A cohort is defined as all same-aged members of a particular population. Because it is difficult to ascribe paternity, many life tables are based only on females. You should examine this table in your textbook, being sure that you understand how to read it. Age is given in years in the life of the cohort.
Mortality rate is equivalent to the proportion who die within a particular age interval.
Survivorship is the chance of surviving from birth to the beginning of an age class. Human population records are often very good, but it is much more difficult to prepare life tables for wildlife populations. One can study the survival of marked individuals, but one can overestimate mortality if one underestimates emigration. You can see how difficult this might be to do by considering the effort that would be involved in preparing a life table for all of the squirrels that live on the UIUC campus. The optimal situation is when the ages of individuals are known by morphology and the remains of dead animals are both persistent and easy to find.