nice concern. If cycles are 28 to 30 days regular then before 7th day and after 23rd day are safe times. But this has a high failure rate of about 10% too. Here counting of days is like 7th day means 7th day from when period began.
Day 1 is first day of period.
Condoms take little timebto adjust. But they prevent from pregnancy
as well as infections. So best to get used to them in some time.
All the best