What are safe days? and when am I safe?
Safe days are the days that one can have sex without use of contraceptive and still not conceive.
The unsafe days are the five days before ovulation (because that is how long some sperm cells can survive in the body) and the day of ovulation itself (because the egg cell is fertile only then). So six days a month are unsafe, the other 24 are not. The only problem is that ovulation cannot be precise predicted and may vary for different reasons (stress or illness, also young girls and older women are often very irregular).
So it is first necessary to know how many days -on average- your menstrual cycle is and how regular it is.
If your cycle was always precisely 28 days, your first unsafe day is 11 and the last is 18.
If your shortest cycle was 21 days and your longest 33, your first unsafe day is 4 and your last unsafe day is 23.
You now understand why this method is not very good if you have irregular periods. And also why it is possible to conceive in the first week, while one is still menstruating. But of course that is quite rare.
The safest thing is always consider use of a contraceptive if you want to avoid unintended pregnancy.
Here are some of the contraceptive methods https://lovematters.co.ke/resource/birth-control-methods .