Do you mean translate or fill in the blanks? Here's how it all works:

With fill in the blank, there is a sentence with a missing word. You select it, and then hit "Check". if it is wrong, you chose the wrong word that doesn't fit in with the context.

With translate, a sentence is given. You must translate. All yellow words are new and you can hover your mouse over every word to give an "about" equivalent in English. Also, you can tell me what you got wrong and I can explain. The hints are the hovers.

You mean the ones with the drop-down boxes to fill in a blank space in the sentence? Those are usually to highlight more subtle grammatical points, verb conjugations, noun genders and the like. At level 2 in Spanish I'd venture they're maybe picking the right articles (el vs. la) to accord with the gender of the noun? The words will have been introduced elsewhere in the lesson or previously, but, yes, sometimes it is very hard to remember (can't tell you how many times I whiffed on such questions for Greek verb conjugations...). You'll get the hang of it soon enough. Wiktionary and SpanishDict are good references for things like conjugations and noun gender.

It should tell you why it was right or wrong. I'm assuming you're on desktop, as I haven't seen this exercise on mobile. I would change the topic to troubleshooting so you're more likely to get some help.