There are different types of essays, but academic essays tend to have many shared conventions regardless of sub-genre.
Most academic essays will...
be organized in paragraphs.
include an introduction and conclusion paragraph.
have body paragraphs that each cover one sub-topic. These body paragraphs will include a topic sentence, evidence or more detailed information, and a discussion of the sub-topic.
be double-spaced with an indent at the start of each new paragraph.
be in a standard font and size, such as Times New Roman, size 12 or Calibri, size 11.
be written in an academic tone and style.
Focus on the information/point, be concise and specific with language choices (for example, don't use the word "you" to mean a vague "someone"), limit bias and emotional language, avoid cliches, etc.
Beyond the above conventions, academic essays may have additional expectations. Since there is so much overlap between essay sub-genres and because instructors will often either not label the sub-type or use certain names interchangeably (for example, an analysis essay and an expository essay can mean the same thing depending on the class and professor). So, to determine the rest, I'd recommend just looking at your assignment sheet.
An essay assignment might also ask you to do one or more of the following:
build an argument to try to persuade the reader of a position on a topic.
use outside primary or secondary research.
cite your sources and include a works cited page or reference page.
addresses potential counterarguments.
Additionally, some essay assignments may be asking for your opinion on an issue, but typically in college, they will be asking for you to analyze or explore information with an unbiased approach.
It can be hard to differentiate between opinion and drawing conclusions from the evidence when writing a paper because it may feel like both of them are your belief, but there are some differences. An opinion is your belief about something, which may or may not be based on anything factual. For example, you may have the opinion that pineapples on pizza are awesome or that people should be kind to one another. While you can support some opinions with evidence, such as finding a study on the effects of kindness, opinions don't have to be based on facts. Even if everyone else hates pineapples on pizza, you can still believe they are the best pizza topping.
However, there are times when having an opinion on a topic is less relevant, such as if you were to say, "I don't believe in gravity." While that statement is still stating a belief, it's not a particularly useful one. Your belief, in this case, doesn't actually impact the existence of gravity one way or the other. And, unless you are somehow deep in space while you are saying those words, your world is still being impacted by gravity at that very moment. As Neil deGrasse Tyson has put it, "The good thing about science is that it's true whether or not you believe in it." In other words, facts and data aren't impacted by an individual person's opinion. New evidence can certainly change how we understand certain topics and that happens all the time, otherwise, we would not progress as a society technologically, medically, and so on. And more problematically, a person's individual opinion or feelings on a topic may cause bias issues when conducting research that can skew the results. However, the information, itself, isn't impacted by opinion, so arguing about a topic from the perspective of an opinion is not particularly useful to the discussion or understanding of the topic.
So, if opinions aren't particularly helpful on certain issues, what is it that we're writing about? This is where drawing conclusions based on evidence comes in. Most writing in college will be fact-based, not opinion based. You will be expected to look at the evidence and then draw conclusions based on the evidence. This evidence can be different things, such as the outcome of an experiment in a science class, lines from a poem in a literature class, or statistics from a business class, just to name a few. By exploring and/or analyzing that evidence and information, you will then be able to draw a conclusion about the topic and then present that information in the form of an essay.
The essay might be expository, analytical, or persuasive in nature, but the thesis and the points you are making will be based on that evidence and not opinion. Even in persuasive essays, where an opinion is sometimes appropriate when written for a college class, there will typically be an expectation that the thesis and sub-points are based on conclusions drawn from factual or observational evidence.