This example is an animal study that followed animals for 28 days after treatment. All five control animals survived the entire time. Three of the treated animals died, at days 15, 21 and 26. The other two treated animals were still alive at the end of the experiment on day 28. Here is the data entered for survival analysis.
Note that the five control animals are each entered on a separate row, with the time entered as 28 (the number of days you observed the animals) and with Y entered as 0 to denote a censored observation. The observations on these animals is said to be censored because we only know that they lived for at least 28 days. We don't know how much longer they will live because the study ended.
The five treated animals also are entered one per row, with Y=1 when they died and Y=0 for the two animals still alive at the end of the study.
Data for each animal was entered on one row. So the number of rows with data in a column equals the number of animals in that treatment group.