Learn Italian: Prepariamo l'attrezzatura prima di fare l'immersione. - We prepare the equipment before doing the dive.

This is the golden rule for prima di (before). When the person doing the action is the same in both halves of the sentence ('We prepare' and 'We dive'), Italian uses prima di followed directly by an infinitive verb. You do not conjugate the verb after prima di.

Could I just say prima fare without the di?

No, to say 'before doing something', you must always include the preposition di between prima and the infinitive verb. Using prima on its own just means 'earlier' or 'first'.

In English, we say 'before diving'. Why does Italian use fare l'immersione (doing the dive)?

While Italian does have specific verbs for diving, it is very common to use fare (to do or make) combined with a noun to describe activities. You will see this pattern often, similar to fare la doccia (to take a shower) or fare colazione (to have breakfast).

English usually treats 'equipment' as an uncountable word. Is l'attrezzatura singular or plural here?

L'attrezzatura is feminine singular. Unlike the English word 'equipment', it is countable in Italian. If you were talking about different types of gear for multiple sports, you could use the plural le attrezzature, but the singular is used here for a general set of gear.