〜と言った。 is a predicate. と is used like a quotation particle. So it's like: as for this person, they said this. スーさんは猫が好きですと言った。 Sue said she likes cats. As for sue, she said she likes cats. Same goes for と思います。 スーさんは猫が好きですと思います。 As for sue, I think she likes the cat. I'm not good at explaining because I just learnt this myself but search up what a "predicate" is and it will help you understand a little more. I hope it helped a little. You can find this in chapter 8 of the Genki textbook if you have it. Send me a message and I will send you the information I have on this subject. :)

と is used for many things. It is a grammar topic. 私は友達と公園に行きました。 Me and my friend went to the park. 寿司を食べないと。 I have to eat sushi. 山本さんは「寒い」と言いました。 Yamamoto said: "It's cold". 明日は雨が降ると思います。I think it will rain tomorrow. 彼は先生だと思います。 I think he's a teacher.