Q: Why aren’t dogs good dancers?
A: They have two left feet!
Explanation: Dogs have four feet called paws: two front feet and two back feet. You could also say that they have two right feet and two left feet. Sounds simple.
When you say that someone has “two left feet” it means that they do not dance well, that they are awkward when they dance.
This joke is funny because it plays with the meanings of two left feet: the literal meaning, like dogs have two feet on the left side of their bodies, and the figurative meaning of being a bad dancer.
If you have always wanted to learn salsa, and not have two left feet as a salsa dancer, you could start here: