Well, how can I break this down enough for you.
In English, there are these things called "words", which have various meanings. Some of them are nouns, which represent a person, place, thing, or idea. Some of them are verbs, which represent an action. Adjectives are commonly used to modify nouns, and adverbs are commonly used to modify verbs. Pronouns are sometimes used in place of a noun in order to facilitate speech. Then there are interjections, used to connect various sentence parts to make more complex sentences.
If you put these words together, you can get sentences, but a sentence must have at least one noun or pronoun and at least one verb. "Cat dog" is not a sentence, neither is "ran walked" but "he ran" is a sentence.
Once you get to the point where you understand that words make sentences and words have meanings, you will eventually get to the point where you can use these sentences to express more and more complex ideas.