How does Frost use two types of imagery to help the reader understand the speaker's feeling about his job?
I think by "two types of imagery" you may mean that the poem is symbolic and somewhat allegorical, in that the description and details of apple picking actually can be seen to stand for something else. Analysis of this poem by many critics has suggested that the speaker in the poem might be the poet himself (Frost) and that the chore of apple picking, and the tiredness and somewhat sad frustration indicated at the end of a large amount of work may be compared to the author's feeling about the work of being a poet.
The poem's imagery is very descriptive of the actual work and experience of apple picking and there are many sensual details which support this idea. But the language also works symbolically to describe a lifetime of work writing poetry, as opposed to a short season of work harvesting apples.
Although this poem was written when Frost was a relatively young man (he was thirty-nine when it was published), it imagines a poet further along in his career who wonders if the work, in the end, is worth the labor. The line "I am overtired / Of the great harvest I myself desired" suggests that a life of writing poetry can be exhausting, perhaps mentally and emotionally, and possibly on a practical level, since many poets cannot make their living (which "harvest" is a reference to) from writing poetry alone. Many prolific poets worked at other jobs; for example, Robert Burns worked as a distillery inspector, and Wallace Stevens worked for an insurance company. Frost is not yet at the point where he can have a lifelong perspective, but it speaks to his wisdom and perception that he imagines what this might feel like in the years ahead, and imagines this as an experience to which other poets might relate.