Low-cost, index funds. S&P 500 or Total US Market is all you need. Add in some bonds depending on risk tolerance / age / retirement date.
All good firms offer them now, with some cheaper than Vanguard (Vanguard is the one who started it all - Jack Bogle). They should be fee free to purchase and sell (but don't sell until you need them in retirement). Buy and hold.
OP - do you get a 401k match? You should be contributing whatever amount gets you that - it is free money, a guaranteed 100% return.
If no match, you should still invest as much as you can - remember it will lower your taxable income. $1 into a 401k is only +/- 70 cents off your paycheck.
You can rollover this account into your 401k and select a Target date fund as others have mentioned. January is a good time to start.