Learn Russian: Я хотел было помочь начинающему, но он отказался. - I was about to help the beginner, but he refused.

The word начинающий literally means "beginning" or "starting" (a present active participle), but here it acts as a noun meaning "the beginner." This is called a substantivized participle. Even though it acts as a noun, it still declines like an adjective. It takes the dative case ending -ему because the verb помочь (to help) requires its object to be in the dative case.

Why is the word было used after хотел? Doesn't that just mean "was"?

In this specific combination, было is not acting as the past tense verb "to be." The construction [past tense verb] + было is a special particle phrase indicating that an action was intended, started, or about to happen, but was abruptly interrupted or canceled. Я хотел было translates smoothly to "I was about to" or "I wanted to, but..."

Why use the reflexive verb отказался (refused) instead of the standard отказал?

The non-reflexive отказать means to deny someone a request (for example, a bank refusing a loan). The reflexive отказаться means to decline an offer, back out, or refuse to participate. Because the beginner is declining the help that was offered to him, the reflexive form is the natural choice.

Could we use the imperfective verb помогать instead of the perfective помочь here?