Cannot connect to home Wifi and to the internet

I am new at this and not really tech savy. My problem is that I cannot connect to my secure Wifi at home (problem of authenticity) as well as the public library, in both instances it is for restricted use and both require a password. However when I go to public places like McDonald's I have no trouble connecting to their Wifi and access the internet.
Has anyone experience such problem and do you have a solution? Thanks.

You need to enter the password. May be on a sticker underneath your router.