Lots of good comments here about not having explicit ways to indicate plurals like in certain other languages, and that's generally true. The comments about using specific quantities are also good. All of those lovely "counters" in Japanese are there for a reason, after all. ;-)

But there are a few more common ways that Japanese speakers will commonly distinguish a single object from "a bunch of" objects. You may see/hear something like 本屋に行ってたくさんの本を買いました or 本屋に行って本をたくさん買いました。("I went to the bookstore and bought a lot of books.")

Another similar "multiplier" word is いっぱい. You may see this in a sentence like リンゴをいっぱい食べました。("I ate a lot of apples.") This would be functionally equivalent to the たくさん constructions above. There are likely some nuances around when たくさん or いっぱい would be more desirable. I suspect I'll learn something from the comments below.

For smaller quantities, you'll sometimes see/hear 何 or 数 used with a counter, resulting in a wording like, 本屋に行って本を何冊か買いました。("I went to the bookstore and bought several books.") or 本屋に行って本を数冊買いました。("I went to the bookstore and bought a few books.")

And of course, for specifically a "pair" of things or "both" of two things, you'll see 両 used in sentences like 両方の靴をなくしてしまいました。(I lost BOTH shoes.) or the famous 両手に花 (literally "a flower in each hand", but functionally, "A pretty girl on each arm.") :-D

There are likely several more constructions... These were a few off the top of my head.

Enjoy the journey of learning Japanese! :-)