Does MySQL have a fixed length of char? Why do you say it's more efficient than varchar?

Many tutorials say varchar (here with varchar (5) example, UTF-8 encoding) the data stored in the database is not long, such as you save "AB" and "in", one occupies 2 bytes, one occupies 3 bytes, because in the disk storage when the number of bytes is different, so you need to record the length.
Is the MySQL char still fixed long when it is stored in Chinese? Kai Time Casino
For example char (5) I saved ' abc ' and saved ' big ' MySQL using space completion, one accounted for 5 bytes, and one accounted for 7 bytes.
The number of bytes occupied is still different ah, no still have fragments!

Does MySQL have a fixed length of char? Why do you say it's more efficient than varchar?