Cant get past the first mission in SW3..!!?

In SW3 you don't get mission briefings like in SW1, instead decision points are made by your dialog responses: in short, you need to pay attention to who is saying what. You can still pause the game or speed it up, the hotkeys are the same. Also, SW3's free-roaming style replaces SW1's mission-based style. There is no "purchasing screen" because you do that when you land at a station. There is no invisible base to retreat to between missions; your mothership is the base.

Without knowing where you are I'll assume you meant the portal to Tira where the game starts. When the MSF appear and take out the Triada pilots, listen to what the trigger-happy major said: don't run or she'll nail your hide to the wall.

If you think you're stuck somewhere, take note of who you last talked to, what they said, what you did and where you are before posting here otherwise we won't know what mission you're on and how to help you.