What does "what else" mean here?

What does "have something to do with" mean?

The expression "something to do with" means that something is about, related to, or connected to something else. Ex: I don't remember everything he said, but it had something to do with the letter he received yesterday. Ex: Maybe she didn't commit the crime, but I know she had something to do with it.

What does "in just a few months" mean here?

"In just a few months" here refers to him being told by doctors that he only has a few months to live, and therefore has only a few months to tell his kids what he would like to tell them.

What is "set someone down"?

"Set someone down" means to place someone carefully on their feet. You can also "set something down." This means to place an item down carefully. In this video, the western wind placed Psyche carefully onto her feet in front of a palace. Ex: He set the kitten down carefully in the grass. Ex: Could you set the food down on the table?

Does the word "rein" have the same meaning as "role?"

No, not quite! Here "reins" is metaphorical. The phrase "take the reins" means to "take control," and it comes from when horses used to be the means of transport, and the "reins" attached to them is how you would drive and control the horse. Ex: Can you take the reins on this project? A family emergency has come up. Ex: I decided to take the reins when I saw it was all very disorganized. Ex: Charlie took the reins, and the party turned out really well.

How is it different if I just say "the really important ones are here" without "over"?

There is a slight difference between these two phrases. Saying "over here" indicates that an object is a little farther away from you. Just saying "here" indicates the the object is close to you or right next to you. Ex: All of my books are over here. Ex: She is sitting over there. Ex: I want you to put our dishes here. Ex: I parked my car over there.