Learn Italian: Mi piace l'arte.

In Italian, the verb piacere works backwards compared to English. Instead of saying "I like art", you are actually saying "Art is pleasing to me". Because "art" is the thing doing the pleasing, the verb piace is in the "it" form.

What exactly does the mi stand for?

mi means "to me". Combined with piace, it literally means "to me it pleases". This is why you don't use the regular word for "I" (io) when talking about things you like.

Why do we need the article l' before arte? In English we just say "I like art", not "the art".

In Italian, you almost always need a definite article (like il, la, or l') when talking about general categories, hobbies, or broad concepts. You can't just say Mi piace arte; it has to be "the art" (l'arte).

Why is it written as l'arte instead of la arte?

arte is a feminine noun, so its word for "the" is normally la. However, because arte starts with a vowel, the la drops its a and connects with an apostrophe to make it smoother to say: l'arte.