How does the aes256 encryption algorithm deal with keys whose length is not equal to 32 bytes?

Question

The reason why I ask this question is that we all know that this algorithm will fill the plaintext data into a multiple of 32 bytes,
so how will the key with less than 32 bytes or more be handled?
Because aes256 encryption algorithm is used in many websites or programs,
and usually we don't set a 32 byte password.
In that case, how should the algorithm go on?
Or is there any place where I can perfectly read the algorithms of all modes of aes256?
I am willing to check the source code of the algorithm by myself.

(this is not an advertisement)
but before that, I wrote an encryption algorithm myself.
I named it "sn_aes2048", Its function is:
"if the plaintext data is not a multiple of 256 bytes,
it will be filled with a multiple of 256 bytes, and the key is the same operation.
16 rounds of encryption will be performed by default,
and the data of the key will be updated in each round of encryption.
You may not believe that this algorithm is both symmetric encryption and asymmetric encryption.
Yes, yes, it is an encryption algorithm similar to aes256."

Answer 1

The reason why I ask this question is that we all know that this algorithm will fill the plaintext data into a multiple of 32 bytes,

AES is a block cipher, which must be used with a mode of operation to be used as a general cipher. Some mode of operations (ECB, CBC) require padding (or ciphertext stealing) to be able to operate. So AES - the block cipher algorithm - doesn't do that, and many more modes of operation (CTR, GCM) don't require padding at all.

so how will the key with less than 32 bytes or more be handled?

AES - the block cipher - supports key sizes of 128, 192 and 256 bits, and that's it. It doesn't perform any actions on the key itself.

and usually we don't set a 32 byte password.

Yes but a password is not a key. Both are secrets, but there are different requirements for keys and passwords. You can indeed use a password based key derivation function (PBKDF) as has been commented below. Other methods exist as well such as PAKE schemes.

You may not believe that this algorithm is both symmetric encryption and asymmetric encryption.

I don't believe it can be any good if you don't even understand the concepts of a symmetric key and a password - or the concept of padding which you're trying to re-invent, but feel free to publish a paper.

Or is there any place where I can perfectly read the algorithms of all modes of aes256?

Try "block cipher mode of operation" and "Padding" on Wikipedia for a start. Then buy a book or follow a course on Cryptography. It is an academic field - creating your own algorithm from scratch is like screwing together your own automobile.