They have the exact same objective, which is to take the enemy team's flag from their base and capture it for your own.
There's a lot going on between captures, such as fighting in the middle of the field, returns of flags, less talented players with no resilience grabbing the flag only to get demolished in a second, you know, things of that nature.
A good WSG & TP strategy that always works (well, it's always good) is to have your entire team going for the enemy flag at the beginning of a game, then on the way back separating with your team's flag carrier and 2 of your healers, to then have all your team's DPSers go retrieve your team's flag, while your team's flag carrier and 2 healers stay as far away as possible from the group of friendly DPSers and enemy team.
If this strategy is executed properly, chances are very high that you will grab a victory.
The philosophy here is to group survival as one, and damage as another.
Your flag carrier and the two healers is survival, they'll have time to call for backup before they get overrun by enemies, and the DPS group will come to assist them.
The damage group is purely damage and CC.
They can use their offensive super-power as a defensive power as well, if they play their cards right, by unleashing an extreme amount of damage which would force the enemy into a defensive state.
In PuG (pick up group) Battlegrounds, you don't want to fight in the middle, but in Rated Battlegrounds, on the other hand, you sometimes get assigned to thin their numbers in the middle, often when the enemy is gathering up to prepare for an attack on your team's flag carrier(he who holds the enemies flag).
You should never really go anywhere alone, if you have died, then make sure that your group (whichever you are assigned to) gathers up near the graveyard before you go anywhere.
It's not worth getting beat up by yourself in the middle of the field because you were trying to reach another one of your team's group.
When you go as a group of DPSers to retrieve your team's flag, make sure that you all open with CC on the ones you're not nuking.
You should always begin with nuking the healers just because they probably have a lot of defensive cooldowns that they can use on the tank.
Before starting to nuke down these healers, your entire team should focus on CCing the people around you in any way possible.
Then you start nuking, and during your nuke, CC anyone who breaks free from an old CC if you can.