Open Roth IRA at Vanguard, deposit $5,500 for 2014.
Is your timeframe at least 15 years?
Can you stomach a 50% drop in the market, if you know that long term, you will beat bonds?
If so: put it all in Vanguard Total Stock Market (VTSMX)
If not: Pick a target date fund or other fund with less expected price swings, but lower long-term returns.
On January 2nd, deposit another $5,500 for 2015 into the same fund.
Don't worry about multi-fund diversification until you have at least $50,000 invested.