Learn Turkish: Gece çok gürültülü olursa diye çantaya kulak tıkacı koydum. - I put earplugs in the bag in case it gets very noisy at night.

Both forms are used for precautions (meaning 'in case...'), but they have a slight difference in nuance. Using the conditional form olursa diye ('in case it happens') treats the situation as a distinct possibility that might or might not happen. The aorist form olur diye ('thinking it will happen') often implies you strongly expect it to happen. Here, the speaker is just preparing for the possibility of noise.

How exactly is olursa formed in this sentence?

It is the verb olmak (to be/become) plus the aorist suffix -ur and the conditional suffix -sa. Together, olursa means 'if it becomes' or 'if it happens'. When combined with diye, it creates the precautionary meaning 'in case it becomes'.

Why doesn't kulak tıkacı have an accusative case ending since it is the object of koydum?

It is the direct object, but it is indefinite (meaning 'earplugs' in general, not 'the specific earplugs'). In Turkish, indefinite direct objects do not take the accusative case suffix. The -ı at the end of tıkacı is actually the possessive marker used to form the compound noun kulak tıkacı (earplug), not the accusative case.

The dictionary word for plug is tıkaç, so why is it spelled tıkacı here?