I'm a fairly new (eight months) Bitcoin owner, so have not had a long history owning it, but have been interested in it for some years. I'm also an old guy (78 years) which definitely puts me at a disadvantage with such a technical product. I've got a few questions about Bitcoin, and thought this would be a great place to get some answers.

1. I've heard a lot about the process of mining, and how miners are rewarded for their work with Bitcoins, but it's the process of mining I don't understand. I do know there's a great amount of computing power, and energy, required, and I'm aware the process validates a Bitcoin transaction,with Bitcoins being the reward for that validation, but what exactly is taking place to make that validation, and how does the system both determine it's a valid transaction, and also detect a fraudulent transaction?

2. How are the individual transactions distributed among the miners?  I know that computing speed is critical, but is it a race to validate a particular transaction among multiple miners at the same time, or are the transactions assigned to individual miners? If it's a race, does it mean a miner can do all the work but then get beaten to the finish line and not get any benefit from his work?

3. What happens to an individual Bitcoin when it's split? Is it a situation where a Bitcoin can be reassembled from it's components after it's been split, or will the splitting just continue until all that remains are billions of tiny components?

I'm sorry if these are silly questions, but I really appreciate getting some help to understand the Bitcoin world a little better now that I'm a part of it.