Help On Something (Think Easy For Most Of You)

Ok im new playing guitar..
and i have a question

ill try to learn/play some tabs:

how do i play the part with 3 strings at the same time,
i must play these 3 at the same time or first one,then the 2nd and then the 3rd

help and any advices with this if i must play em' @ the same time?

At the same time. If you look at one of them:

Play the 5th fret with your index finger, and then the 7th fret with your ring and pinky fingers. Get used to this chord if you're planning on playing a lot of rock based stuff.