Learn Turkish: Bu oturumu destekleyecek sponsor büyük bir şirket. - The sponsor who will support this session is a large company.

It uses the future participle suffix -(y)ecek. While it looks exactly like the regular future tense, here it sits right in front of the noun sponsor to describe it. In Turkish, putting a verb in this form directly before a noun turns it into a relative clause acting as an adjective: "the sponsor who will support".

Why does oturum (session) have the accusative suffix -u (oturumu)?

Even though destekleyecek is acting like an adjective to describe the sponsor, it still behaves like a verb internally. Because "this session" is the specific thing receiving the action of being supported, it acts as the definite direct object of destekle- (to support) and must take the accusative case.

Where is the verb for "is" in this sentence?

There isn't a visible one! In Turkish, you can form "A is B" sentences simply by placing the subject next to the noun phrase it equals. The subject is Bu oturumu destekleyecek sponsor and it sits right next to the predicate büyük bir şirket. The "is" is implied.

Why is the word order büyük bir şirket and not bir büyük şirket?