"Mom does not have a dog."
Translation:У мамы нет собаки.
The phone app doesn't show the tips and hints, but you can use your phone web browser to log in to the web version of duolingo, and open them from the web view of the Russian course.
As an added bonus, the horrible pale yellow of the new words on the web version is a little more distinct and readable at night on a dimmed phone.
It's so frustrating that even as of 2021 the Tips are not available in the phone app for Russian but are available for many many other languages including Chinese and Japanese! The tips would cut down on the amount of questions and the amount of the same questions here in the forums. Not to mention the many frustrations! = (
not quite. есть can be omitted before много: У меня много книг = У меня есть много книг. (I have many books) Both are correct. Нет on the other hand is a verb "not have" - it absolutely can't be combained with есть. You can use не есть, usually as a phrase Это не есть хорошо (It's bad), but it's more of a slang expression.