Hi,

how can I control the main motor from SATA pins directly?

The point is just simply make it spin.

Like this:

[www.youtube.com]

...or if someone can explain what bridges to make in circuit itself.

In the example video you provided they use only power, not the signal cables. If you mean creating something similar you have to hack the driver (like they did on the video).
If not you can send control signals directly to sata drive to make it spin up.