Encrypting AES in ECB mode
Here are some things to keep in mind


AES encrypts bytes, not characters. So you have to transform your plaintext into bytes. How are you going to do that?
In AES, a block is 128 bits. That is 16 bytes. If your plaintext is only 8 characters long, and each character is encoded as 1 byte, you are short 8 bytes. You can add some padding (a 1 followed by all 0's, something like that).
ECB mode is insecure (except maybe in some very specific use cases). That being said since you are only encrypting less than 1 block, and you are just doing it to try to learn AES, you shouldn't even really be concerned with a mode-of-encryption at this point. Just focus on AES running on a single block.


Without more information on where you are getting stuck, there isn't much more help I can give.