New to the game and it seems pretty simple to understand but there's one thing that I have a question on...

During the conflict phase if my opponent attacks with only a vehicle unit can I block with a character unit or do I have to have a vehicle unit out as well? Also the same question the other way around, if I attack with a character unit can my opponent block with a vehicle unit or do they have to have another character unit?

Defenders and attackers do not need to match unit type.

Under normal conditions, any ready unit can be assigned a a defender against any attacking unit.

There are a few card effects for which the unit's trait might be a factor, but then it will be clear from the card text which units can or cannot be used to be declared as defenders.