This answer is specifically about your statement "….the RSA-algorithm aka how things are encrypted/deciffered." RSA usually isn't used for encryption, and when it is it's never just the RSA algorithm. AES isn't used alone for encryption either!
AES is a symmetric key algorithm, specifically a block cipher. It takes a key and an input block, and produces an output block. Using the same key on the output block produces the original input block. With AES, blocks are 128 bits (16 bytes). Keys are 128, 192, or 256 bits. They must be chosen uniformly at random, but other than that don't have any restrictions.
AES can be used to build an encryption scheme, but by itself isn't used for encryption, since it can only encrypt a single 16-byte block securely! It must be used in a "mode of operation" to usefully encrypt anything bigger or smaller than 16 bytes. AES can also be used to build cryptographic hash functions (no common hash does this, but AES-Hash was proposed), message authentication codes (AES-CMAC), key derivation functions (NIST SP 800-108 describes how), and more. It's therefore wrong to consider AES (or any other block cipher) as only an encryption function, despite the "encryption" in the name.
RSA is an asymmetric key algorithm. It has two keys, a "public" key and a "private" key. The public key is assumed to be publicly available, the private key is assumed to never be shared with anyone. The RSA operation uses one of the keys, and can be reversed using the other key. RSA keys have specific mathematical structure to make this possible; private keys are chosen first and the public key is derived from the private key. This Wikipedia article describes RSA key generation well, but the specifics aren't important for this answer.
Like AES, RSA is not used on its own for encryption. It must be used with a "padding scheme" for encryption. Even with that, it's quite slow and limited to encrypting a few hundred bytes at a time for practical key sizes. RSA is more commonly used to build a signature scheme (again with a padding scheme), though it's sometimes used to build a key exchange mechanism to exchange symmetric keys (eg for use with AES in the Galois Counter Mode of operation).