Your thesis statement provides the reader of your essay with an overall statement about what you will be proving. It could be something along the lines of, "I learned Spanish as my first language by growing up in Colombia, and when I learned English to attend high school and college in the United States, my knowledge of Spanish grammar, the differences between spoken and written language in Spanish, and my ability to write in Spanish all helped me learn English." The first paragraph in your essay would include more background about your first language and when and why you started to learn English.
Each later paragraph in your essay would examine in further depth one of these points. For example, in your first body paragraph (which comes after the introduction), the topic sentence might be something along the lines of, "My knowledge of Spanish grammar helped me learn English." The topic sentence contains the main idea that you will discuss in that paragraph--in this case the reason why learning your first language (or languages) helped you learn other languages. The paragraph would flesh out this idea and include more details about how learning grammar in your first language helped you learn English grammar.
The next body paragraph might begin with the topic sentence "Learning the differences between spoken and written language in Spanish when I was younger helped me understand these differences in English." The rest of the paragraph would include details about this point. The third body paragraph might start with the topic sentence, "My knowledge of how to write in Spanish helped me learn to write in English," and then the rest of the paragraph would expand on this idea and provide details to support it. Finally, you would conclude your essay with a concluding paragraph that restates your main idea.