Learn Turkish: Heyecanımızı azaltmak için hazırlıkları bitirelim. - Let's finish the preparations to reduce our excitement.

It comes from heyecan (excitement) + -ımız (our) + -ı (accusative case marker). It needs the accusative case because it is the specific direct object being reduced by the verb azaltmak.

I thought için meant 'for'. Why does it mean 'to' here?

When you pair a dictionary-form verb (ending in -mak or -mek) with için, it creates the meaning 'in order to' do that action. So azaltmak için means 'in order to reduce'.

Why does hazırlıkları end in -ı?

The root is hazırlık (preparation). We add the plural suffix -lar to get hazırlıklar, and then the accusative suffix -ı. The accusative is required here because 'the preparations' are the specific direct object of the verb bitirelim.

What gives bitirelim the meaning of 'let's finish'?

The verb stem is bitir- (to finish). The -elim ending is the first-person plural 'optative' suffix, which we use to say 'let us' do something. If the verb had back vowels, we would use -alım instead.