1. How does the Bitcoin network guard against hackers seizing control of the system?
To control the Bitcoin network, not the system, attackers (not hackers) will have to own 51% of the network hashrate. If they own less than 51% of network hashrate, their attacks will very less likely succeed.
2. How do miners fit into the Bitcoin network?
Have ASICs, run their full nodes, and mine Bitcoin blocks as solo miners or they can join mining pools.
3. How is fraud prevented on the Bitcoin network by transaction verification?
Transactions will be confirmed by miners but each new block will be verified by many nodes on the network.
4. What distinguishes a private key from a bitcoin address?
They have different formats, length, starting characters.
Keys, Addresses