Capital gains

I sold my home on April 1st and made a $90,000 profit. Unfortunately I was only in my house q8 months because I had no idea I moved next to drug dealers! So I sold it. I am looking for another place and living with friends for now... but wanted to pay my capital gains tax (I understand I have to pay this for living in a house less than 2 yrs)  and want to know:

1- what forms do I need?

2-how much do I owe? (I assume at my income level it will be 15%) 

3- can I pay this NOW instead of at the end of the year so that I know how much I have to work with for a down payment on a new place?

R-how?

Thank you kindly! 

Phillis