If a model is Prone it suffers a -1 Melee Pool modifier and does not block LoS.
Enemy models may ignore it’s ZoC and may choose not to be considered in BtB with them when declaring or performing their actions, meaning the action choice is not restricted by being in BtB with the Prone model.
Prone models are always the Attacker second in Melee Exchanges, and may not use Special Abilities or benefit from traits or effects that affect Initiative.
The only action a Prone model may declare is a Stand Up Action.
If a Prone model initiates a Melee Exchange through taking a Stand Up action, it suffers a -1 Melee Pool modifier for that Melee Exchange, but Initiative is not affected.
A Prone model cannot gain Prone Markers.