be useful
ちょっと言葉を知っていればずいぶん役にたつよ。
It helps a lot if you know just a few words.
この箱は何かの役にたつ。
This box will come in handy for something.
それは本当に役にたつものですから、ぜひ買うべきです。
It's really useful, so you should definitely buy it.
この本は我々に役にたつ。
This book is useful to us.