好（す）き, meaning ‘to like’, is one of the very common な-Adjectives in Japanese that is used in many different expressions. All な-Adjectives behave similarly to verbs, in that their form changes depending on what comes after them.
For 好（す）き, it will be followed by either な, when acting as an adjective, だ, or the more polite です, when acting as a noun. This distinction is made depending on whether it is linked to another noun, or is independent.

• 私（わたし）はコンビニが好（す）きだ。
  I like convenience stores. (They are likable, to me)
• 彼（かれ）はサーフィンが好（す）きです。
  He likes surfing. (It has likability, to him)
• 私（わたし）が好（す）きなピザを食（た）べる。
  I eat the pizza that I like. (The pizza that is likable, to me)

In the example with だ, 好（す）き is expressing that the thing is ‘likable’ (assertion). However, in the example with な, 好（す）き is expressing ‘likability’ as a quality of the noun it is attached to.