In English, its common to say:
He was helpful.
In mandarin, we need to explain what he did was helpful. For example:
If he gave you helpful suggestion, we would say “His suggestion was helpful”
If information he found online solved your problem, and you cannot simply say "he is helpful." we have to say“The information he found online was helpful.”… etc.
Here is a mistake of a student.
He wrote: The colleague is nice and helpful.“”
In mandarin, we say : The colleague is nice. His suggestion was helpful.
“Zhè gè tóngshì hěn hǎo这个同事很好。 Tā de jiànyì hěn yǒu bāngzhù 他的建议很有帮助“