The imperfect is a form of past tense that’s pretty common in the Romance languages.
English doesn’t really have it and German doesn’t either, so don’t worry about it.
With the pronunciation tool, you can check how well you pronounce a word or sentence. It uses an AI system that is being developed by EF languages for that purpose. The AI takes your input, and compares it to how a native speaker would sound. Then, it gives you feedback for each word and the sentence as a whole.
You put in a word or sentence or load and example from the site. Then you hit record to start and again to stop. You'll then get feedback on how you did, for each individual word and in total. The AI grades sound, emphasis and rhythm. The recording is limited to 20 seconds and will stop automatically.
That's beyond what an automatic system like this can do. It's not a tool to perfect your pronunciation. It's more about giving you a rough estimate and giving you the option to actually speak. But to really iron out mistakes, you need feedback from a native speaker.
Quite a bit depends on the quality of your microphone. If there's a lot of noise around you, the AI will struggle with that. Also, the AI does better with sentences. For short words, it's not as good. Lastly, the AI is still being developed and struggles with some important words.
The recording button should change color and pulsate while recording. If nothing happens, the most likely problem is that your browser is blocking the microphone. You can allow mic access by clicking on the icon left of the address in the address bar (on most browsers).