How to mod:
1.) Go to the tutorials forumn (or the newbie question forumn)
2.) Click on the subject you think would be relevant
3.) Try the tutorial.

The question 'how to mod' is so wide, it would takes hundreds of posts to explain.
there are tutorials for just about everything you would want to do.

Okay will do!

I tried to add a big bad ship already. By me it was the rheinland battleship. But i had bad experiences.
1., The camera positions are so bad, that you can only fly a cruiser in Turret View to see what happens around you.(not to mention fighting!!!) I could not fix this.
2., The ship is big. No. HUGE. It wont fit the docking rings. I got bored to figure out, how to use moors. I gave up. There is mod called Ghost Docking Ring. Huhhh.
3., I succeded to create huge ship turrets and clould mounted. Even to the small ships. That was funny
4., Such a ship is hard turn. It takes kilometres to get a corner. Just imagine.

Still, i think i'll try that again later. Much later.