Ok so I was just watching a let's play of birth by sleep,

And this dawned on me when terra first learns of vanitas from master x, then he gets a vision of aqua and ventus when ven is about to fight vanitas right after vanitas knocked aqua out and was about to stab her and ect.

So my question is, is that can terra see the future? or can he see sinp-its of it?

Or what

Nope.

What's the meaning behind the several puzzling images in Terra's chapter where we cross over into his mind?

Nomura: Firstly, when he hears the name of the masked boy from Master Xehanort at the mysterious wasteland, and we see an image of Aqua and Ventus defeated, that's a hint of the future. On the Destiny Islands, when he makes Riku his successor, he has a special view of him and catches a glimpse of his future. However, this isn't to say that Terra has the ability to see the future - it was a directive nuance intended to portray the future connection between Terra and Riku.

It's a shame he can't.  Then he would have known better than to trust Master Xehanort

that would another shitty plot point to birth by sleep and its totally stupid