It’s user-generated content. So if someone else has researched their family, and it happens to include your family, the details will be there. Otherwise…it’s on you.
No, it has official records - births, marriages, deaths, census records and much more. But you have to start by putting in some information that you already know. You can start with just the name and date of birth or death of a grandparent.
For example if you know you had a relative called Frank Smith who died aged 75 in 1990, you could search the 1921 census for a Frank Smith who was aged five or six then. If he was at home with his parents on census night, you will find his parents, siblings, anyone else in the household, their ages and birthplaces.
Then you can search for his parents' marriage, and also look for them in previous censuses, and so on back through the generations.
When I started family history, it was way before the internet. There were excellent books one could buy which told how to go about it and what sources were available. I don't know what guides are available now. But you ideally need to know what you're looking at before you begin.