I'm New to Imperial Assault After playing a side mission, The mission card says for the reward "Reward Card" does that mean that all the rebel players get a reward card? if they win that Mission.

Thanks Tim

In the text at the end of the mission it should give the name of a specific reward card (e.g. if the rebels win the mission "A Simple Task" they get the "Adrenal Implant" reward). For most of these rewards the rebels can choose which (one) hero gets to keep the card.

The exceptions to this are the rewards for completing a hero's red story mission. For example if the rebels win Jyn's mission, "High Noon", it's always Jyn who gets the "Peacemaker" reward card.

Also, the reward cards are open information. The rebels thus know what the alternatives are when they are choosing a side mission to play.