Nowadays means in the present time, as opposed to how it used to be. The comparison with the past is built in.
That is what makes it different from now, since nowadays always implies a contrast, which is why it appears constantly in sentences beginning with people. It sits at the start or the end of a clause. The word is a single word and slightly informal. These days does exactly the same job and sounds a little less like the beginning of a complaint.
1adverbnowadaysAt the present time, in contrast to the past.
“Nowadays almost nobody carries cash.”
From now + adays.
Etymology from Wiktionary, CC BY-SA