The dissolve delay is the amount of time you set on the timer until you can get your locked ICP out of your neuron. The dissolve delay value you set has the biggest impact on your voting rewards with longer dissolve delay resulting in higher voting rewards.
Unlocking your neuron is like starting the timer. Locking your neuron is like stopping the timer. It is important to note that unlocking your neuron will reset your neuron age bonus to zero. There is currently not a warning or confirmation in the NNS app, so make sure you are aware of this detail before you click the Start Unlock button.
Maturity is a ratio of ICP voting rewards earned divided by ICP staked in the neuron expressed as a percentage.
Staking is the process by which you lock away your ICP in order to be able to govern the Internet Computer Protocol by voting on NNS proposals.