Vpn ipsec question beginner

[Saldebob]

Hello,

I am looking at the basics of the network and I have a question.

1)In phase 1 of an ipsec tunnel there is a key What does this key correspond to

2)In phase 2 there's another key, what does it correspond to

3) Despite my numerous internet searches, I still can't understand what IKE and ISAKMP are in simple terms

4) why do we say that the security parameters are negotiated between the 2 peers when we define them manually?

Thank you very much.