Learn Polish: Ten drogi garnitur bardzo mu się podoba. - He likes this expensive suit very much.

The verb podobać się translates better as "to appeal to". Instead of saying "he likes the suit", Polish says "the suit appeals to him". mu is the form of on (he) that means "to him".

If the English translation starts with "He", why does the Polish sentence start with Ten drogi garnitur?

Because podobać się works like "appeals to", the thing being liked is the actual subject doing the action. Ten drogi garnitur (This expensive suit) is doing the "appealing", so it naturally takes the main spot at the start of the sentence.

Why are mu and się placed next to each other in the middle of the sentence?

Both mu and się are short, unstressed words (often called clitics). In Polish, these short words hide in the middle of the sentence, usually right after the first or second main piece of information. They almost never go at the very end or the very beginning of a sentence.

How do we know to use ten drogi instead of other forms like ta droga or to drogie?

Words that describe a noun always have to match its gender. garnitur (suit) ends in a consonant, which makes it a masculine noun. So, we must use the masculine forms for "this" (ten) and "expensive" (drogi).