Lewis Carroll's "Jabberwocky" is a nonsense poem. While many of the words may not make sense to a reader, Carroll's poem is still written using conventional grammar. The main parts of speech one can identify within the poem are nouns, verbs, and adjectives.
In order to begin to define parts of speech, a reader must be familiar with what a noun, verb, and adjective is. A noun is a person, place, or thing. A verb shows action. An adjective describes a noun.
To begin, let us examine the first "sentence" of the poem:
"Twas brillig, and the slithy toves did gyre and gimble in the wabe."
The nouns in this sentence are "toves" and "wabe." In order to justify this denotation, let us examine the word's placement in the sentence. First, ignore "twas brillig, and." "The slithy toves" speaks to the subject of the sentence. Within a typical sentence, the subject contains the noun. In this case, the noun would be toves and the adjective would be "slithy" (because it describes the toves).
"In the wabe" is a prepositional phrase (tells how, where, when). In this case, it tells us where the toves are. Since "wabe" refers to a place, it is a noun.
In order to state what the toves did in the wabe, one must look between the two words. According to the sentence, the toves "did gyre and gimble." Although these are nonsense words, one can identify them as verbs. These words appear in the predicate of the sentence (which is where the verb will appear).
Therefore, although the poem seems to make no sense at all, Carroll's use of conventional grammar allows one to readily identify the parts of speech within the poem's lines.