Tabula Rasa will have a working PvP system at the games launch providing all levels of players content to participate in.

Are there "Open PvP areas?"

All PvP at this point is consensual. Developer Paul Sage explained in a Developer Diary that:

"It was important to us in developing the PvP system in Tabula Rasa that the approach we took allowed for players to voluntarily take part in PvP, yet still allow for players to engage in the surprise type of ambushes that makes large scale PvP so exciting. As a result, we took a multifaceted approach to the PvP in the game"

What is a Wargame?

A wargame is essentially a duel, but the difference between this and your ordinary duel, is it can be between squads. According to Paul Sage:

"During a wargame, players will have the opportunity to challenge one another and decide, after viewing a summary of the other participant's stats, whether or not to accept the challenge. While on a squad, only the squad leader can offer or accept a challenge to a wargame. Once engaged, the wargame will last until one side wins or surrenders. But, the players should remember that these skirmishes are taking place in the middle of an intergalactic war. So, if the players happen to come under attack by enemy forces, they can still be attacked and killed, at which time they would lose the wargame. Those are the breaks for fighting within the AFS ranks in enemy territory."

What is Clan vs Clan?

A clan performs the same functions as a guild in other MMOG's. You can join one and declare war on another clan allowing open warfare between the two. This type of system is semi-consensual, being only the leaders can declare war, but there are PvE based Clans you can join which don't participate at all.

Paul Sage stated that Tabula Rasa's PvP system "lends itself to additions and variations in the future, like wagers, 'Capture the Flag', and other player driven developments.

Will this mean Battlegrounds, Arena, or other popular mechanics used in other games? Little more is known at this time, but it doesn't sound like they are done.

There has been no mention of all PvP servers available when the game launches.