Learn Polish: Lubię robić zdjęcia.

In Polish, you "make" a photo rather than "take" it. The fixed phrase for "to take photos" is robić zdjęcia. If you used the Polish verb for "to take" (brać), it would mean you are physically picking up printed photographs with your hands.

Is zdjęcia singular or plural in this sentence?

It is plural, meaning "photos". The singular form is zdjęcie (a photo). It is in the accusative case here because it is the direct object of the verb robić. For neuter nouns like this one, the plural accusative form looks exactly the same as the plural dictionary form.

Why is robić left in its dictionary form instead of being conjugated?

When you express liking an activity, you use the conjugated form of lubić (here, lubię for "I like") followed directly by the infinitive (dictionary form) of the action verb. This is similar to saying "I like to take" in English.