In UTF-8, your standard latin characters are encoded just as they are in ASCII (1-byte each), and all UTF-8 characters are 1-4 bytes. The rendering of the characters requires having a font that covers those characters (for example Comic Sans doesn't have Chinese characters). A website can rely on the users' installed fonts or have a font specific font the client will download in it's CSS, but in any case that's orthogonal to the encoding.
https://en.wikipedia.org/wiki/UTF-8#Description