havent done anything car audio related since high school but i want to put a 10" sub in my car and maybe some tweeters, exhaust is too loud now cant hear my music

2012 bmw 135i nothing done to the sound stuff, and i have no idea what the stock setup is+

what do i gotta do and how much is it gunna cost me

adding tweeters turn this into a big ordeal and certainly not worth the effort. replacing the speakers already installed is a much better choice.

adding a subwoofer is straightforward however and requires very little work to do.

https://www.sonicelectronix.com/item_46220_NVX-XPLOC2.html one of these lets you turn speaker inputs into rca inputs for the amplifier.

now as for the rest it really depends on how much you want to spend.

prebuild boxes run $40-60 typically
subwoofer prices vary depending on quality and power.
amplifier prices are the same as subwoofer prices.

an example of a good cheap setup would be

https://www.sonicelectronix.com/item_32005_Atrend-10SQV.html
http://store.soundsolutionsaudio.com/products/sound-qubed-hds210-10-inch-subwoofer.html
https://www.sonicelectronix.com/item_67758_Rockford-Fosgate-Prime-R500X1D.html
http://www.knukonceptz.com/mobile-audio/amp-installation-kits/sp/kca-complete-4-gauge-amplifier-installation-kit-/

I've been trying to put a tweeter or speaker in my gashole

with that rca adapter i still need to run a remote wire from the headunit?

it's built in. saves that headache lols.