It is very simple to open an account.
If you only want to put your Roth funds in to a bank account or Certificate of Deposit, many local banks or Credit Unions can open a Roth IRA for you.
If your are interested in mutual funds or ETFs any one of the major investment companies can create an account in a matter of minutes. The large companies have dozens of funds for you to invest in.
If you want to trade stocks, then there are companies that can do that also.
Some companies can fill all three roles.
Here is the best thing about a IRA or Roth IRA. If you decide that later you want to change companies, or investment styles: selling the funds/stocks you have and rolling your funds into a different investment or even to a different investment company can be done and will not trigger a taxable event.
So take little time, you have about 90 days before the IRA window for 2015 closes an tax day, Pick a investment company that has many investment options, that has low initial investment requirements, and has low fees. Once you have done so, open that account and pick an investment vehicle, and put your Roth funds into the account.
Note: don't wait until the last week to open and fund the IRA. They can be very busy and you wouldn't want to miss the deadline. Also realize that you can file your tax form before making the actual investment. Many people use the refund to help fund the IRA/Roth IRA.