Most developers do not need to understand the internal math of AES to use it correctly. What actually trips people up is the handful of terms that show up in every AES-related API: key, IV, mode, and tag. Here is what each one means in plain language, without the cryptography theory that usually gets attached to explanations like this.
AES stands for Advanced Encryption Standard. It is a symmetric cipher, which means the same key is used to both encrypt and decrypt data, unlike an asymmetric system like RSA that uses a separate public and private key. AES has been the industry standard since the early 2000s, is used by governments, banks, and basically every major piece of software you interact with daily, and has no known practical way to break it when used correctly. The phrase "used correctly" is doing a lot of work in that sentence, which is why the rest of this article matters more than the algorithm itself.
This is the secret value that both encrypts and decrypts your data. AES supports key lengths of 128, 192, or 256 bits, commonly written as AES-128, AES-192, and AES-256. A longer key means more possible values an attacker would need to search through, so AES-256 is generally the safer default when you have the choice, though AES-128 remains secure against any currently known practical attack. Never reuse the same key across unrelated purposes, and never hardcode it directly in source code that ends up in version control.
An IV is a random value used alongside the key to make sure that encrypting the same plaintext twice produces different ciphertext each time. Without it, an attacker could spot patterns by noticing when two encrypted messages are identical, which leaks information even without breaking the cipher itself. The IV does not need to be kept secret, but it does need to be random and, critically, it must never be reused with the same key. Reusing an IV is one of the most common real-world AES mistakes and can seriously weaken the encryption.
AES encrypts data in fixed-size blocks, and the mode determines how those blocks are chained together for messages longer than one block. The two you will run into most are CBC, which chains blocks together using the IV but does not verify integrity on its own, and GCM, which adds a built-in authentication check on top of the encryption. Unless you have a specific reason to use CBC, such as interoperating with an older system that requires it, GCM is the better modern default.
This one only applies to authenticated modes like GCM. Along with the ciphertext, GCM produces a short tag that gets checked during decryption. If the ciphertext, IV, or tag has been altered in any way, decryption fails outright instead of silently returning corrupted or tampered data. This is what people mean when they say GCM protects both confidentiality and integrity at once, rather than only hiding the data from being read.
In practice, a correct AES-256-GCM setup means: generate a strong random 256-bit key, generate a fresh random IV for every single encryption operation, never reuse that IV with the same key, and check the authentication tag on decrypt before trusting the result. You can see all four of these pieces working together on the Encrypt / Decrypt tool on this site, which generates a fresh IV automatically for every operation and runs entirely through the Web Crypto API in your browser.