Most college-level writing involves academic papers, unless you're writing fiction or other rarer types. An academic paper is something written by a scholar, in this case you, for other scholars. While you technically usually write just for your teacher, the paper should be geared to your peers. The topic of your papers is something of interest to other scholars and researchers. In the paper, you should make an informed argument, garnered through reading and research.
The structures of your papers will also most likely be different from your high school papers. Many high school students rarely write a paper of more than a few pages long, but in college your papers might be several pages long. Your professors will give you structure instructions that might vary from class to class. But, in general, your paper should include an introduction that introduces the argument for your paper and puts it into context. Supporting paragraphs will back up your argument. Your conclusion should sum up the paper but not simply repeat everything in the paper.
In an academic paper, you write analytically, meaning you critically look at a situation and evaluate it using appropriate sources. Stay away from using personal pronouns like "I" and "me." Also don't speak directly to the reader and use "you" or "your." Use proper grammar and spelling and make sure to proofread all work carefully. Also make sure that your writing is clear and doesn't contain unneeded words or phrases.
If you struggle with college academic writing schedule an appointment with your professor to talk about assignments and visit any sources of help offered on campus like writing labs. Make sure to read all instructions carefully. Some professors are detailed about expectations including font sizes and type. Don't write your opinions, or what you can't prove, unless specifically asked by your professors. Colleges take plagiarism seriously. Make sure to cite your work and also never copy directly from a source without using quotes and attribution.