"He has a book and a newspaper."
Translation:Tá leabhar agus nuachtán aige.
You should read the Tips & Notes associated with each lesson on the website - click the light-bulb icon in the popup when you select a skill. The sentence structure and the way to say "have" in Irish are covered in the Notes of the first 3 skills in the course.
You can access these Tips & Notes in the browser on a mobile device too, even if you are using one of the various Duolingo apps.
I have the same experience as Kelly7299241. I can’t see what I wrote so that I can see what I got wrong. As soon as I press submit, my answer turns a light grey color which is hard to read and is usually partly or completly covered by the correct/incorrect pop-up window. The same thing happens in all my other courses. I’m using the browser version on an iPhone, not the app.
This is what a wrong answer looks like in the browser on my phone:
I've never seen anything like what you're describing, so I have no suggestion for how you should deal with it. And realistically, the Sentence Discussion for "He has a book and a newspaper" isn't really the best place to look for advice like this - you'd be better off posting in the Troubleshooting forum.
You use tá at the beginning of the sentence when tá is the appropriate verb for that sentence - the basic structure of an Irish sentence is Verb-Subject-Object.
Irish doesn't have a verb that means "have", it uses the tá ... ag to express the same idea - tá X ag Y - "Y has X". Therefore tá is the appropriate verb for this exercise, and it goes at the beginning of the sentence.