Newbie to Hair Care Need Help

I need LOTS of tips on making my hair somewhat manageable.
It's dry, thick, and is very painful to comb or brush. I don't know what to do.

It never stays in once place; and it's just too much hair to deal with.
Can't wear disheveled pony tails for the rest of my life.

I just want it straight like my little sister.

It's flat and and manageable even when it's so called nappy.
It's like magic the way she can make it straight with pink hair spray stuff and a flat iron.

I don't even leave the house anymore because this is so frustrating and no one will help me.

Anyone got any tips? I'm two seconds away from shaving it all off.