To Be Useful, To Be Of Use, To Be Helpful, To Be Of Service
godan verb
When you stand up to do your duty you're standing up and finally being useful. That's why this verb means to be useful.
やくにたつ
The reading for 役 is the one you learned with the kanji. The 立つ reading is that of the 立つ vocabulary, which you should be familiar with by now.
マスキングテープは、色々なことの役に立つ。
Masking tape is useful for various things.
山下先生の助言は、人生の役に立つ。
Yamashita-sensei's advice is helpful for life.
あまりお役に立てず、すみませんでした。
I'm sorry that I couldn't be much help.