I got a 250 2002 ninja. It won't go into gear and I need to rebuild the engine because it smokes a lot. What would be my first step to fixing it? I'm a chick that doesn't know too much about fixing a ninja but have knowledge of the parts and there locations

On higher mileage engines the internal parts are very worn such as piston rings. This can allow small amounts of oil into the ignition chamber. This burns off as you run the engine.
If the amounts of smoke is small and not very often it is nothing too serious to worry about. If there is a lot of it and it regularly happens, the only way to fix the problem is to completely dismantle the engine and rebuild it with all new seals and gaskets, a full engine rebuild.

White smoke mean burning coolant you most likely have oil in radiator. With the low power the engine is low on compression. I would say vehicle is going to need a new engine or a engine rebuild

If it is gray or oil smoke you are obviously burning oil - probably your piston rings/ you need to rebuild the engine to fix that. You can burn a thicker oil to cut down on the oil consumption but that increases overall friction and lowers mileage. And if you are in a cold weather zone and a freeze hits no way that engine will turn over. Your choice.

from your description the do it your self fix is another motor from the wreckers. If it is a big end there will be crank shaft journal damage and that means major rebuild and lots of dollars
A replacement engine will be cheaper and less costly in the long run.

Don't sound like a fuel pump,replace fuel filter and see if it fixes.

Rebuilding automatic transmissions properly requires a lot of time, skill, training and experience to get it right. A beginner will have little success in making a lasting repair. I have known of experienced professionals fail to fix them properly. An exchange transmission would be the best option, although more expensive, as you should get a warranty and will be out of action for only a short time.

The shifting problem is a bent shift fork. It will only get worse and is expensive to fix. The smoke is probably getting past a exhaust pipe gasket. When you fix the shifting it would be a good time to rebuild the top end with new pistons and rings.

i think you need to replace the 2nd. gear. most likely you have to rebuilt the trany get a good mechanic because need to take motor out of frame and open the bottom part of the engine.