What does mi guapo means?

Lets start with a Word by Word translation:

-'Mi' means 'my' in English.

-'Esposo' means spouse, in this case, a husband since it ends in 'o' (masculine ending)

-'Es' is like 'is' in English.

-'Muy' means very.

-'Guapo' means handsome (and again, it ends in 'o', so it is masculine, which makes sense because the person is referring to their husband)

So when you put it all together:

'My husband is very handsome'