Here's a question that I've been asked many times:
Is it ok to start an essay with 'nowadays'?
The quick answer is yes. There's nothing wrong with this word, and the examiner won't reduce your score if you use it.
But be careful. Not all topics can be introduced with the word 'nowadays'. This word is usually used by native speakers to compare the present with the past e.g. Fifty years ago, only the rich could afford international holidays, but nowadays foreign travel is relatively inexpensive.
My tip: While there's nothing wrong with the word 'nowadays' when it is used correctly, I think it's a bit of a beginner's way to start an essay. If your mind goes blank in the exam, go ahead and use it. Otherwise, I'm sure you can find another way to start your essay.