This paragraph begins with an overall thesis statement that includes the main idea of the paragraph. The main idea is that the land can either heat or cool winds, depending on the form of the land and the water. Therefore, the land can either heat or cool the wind, and the wind is what transports weather.
After this thesis statement, the reader gets additional details, which are that winds from the ocean cool the land near the ocean in the winter and warm land near the ocean in the summer. Part of the reason this sentence is confusing is that it's in the passive tense, meaning that the winds, which carry out the action, are in the clause beginning with "by." It would have been clearer if the winds were carrying out the action in the active tense, such as "winds from the ocean cool the land near the ocean in winter and warm the land near the ocean in summer."
This is a great example of a reading comprehension question. Your job is to find the information the question asks for within the reading sample.
One way to do this quickly is to scan, or read quickly, for "key words". In this question, try scanning for the phrase "land near the ocean". You'll see that it appears once, in the second sentence. You could also try scanning for "winds from the ocean", which would likewise lead you to the second sentence. The second sentence is "Land near the ocean is warmed in winter and cooled in summer by winds from the ocean".
Your teacher probably wants you to rephrase the answer, rather than just directly copy. You can do this by adding related information from elsewhere in the paragraph. In this case, I see in the last two sentences that oceans heat and cool slowly, while land surfaces react quickly. That information explains why ocean temperature moderates land temperature.
The beginning of an answer might be: Because oceans heat and cool slowly while land surfaces react to temperature changes quickly, ....