Not sure what you consider pocket change, but IRA's have a yearly contribution limit of 5,500 a year, so once you put that much in it for the year you're done. If you have more money you want to invest at that point, you need to put it in a regular account, the only difference being is this account is subject to taxes. Once you have money in either account, you need to pick an actual "fund" to put it in. Many sites like Vanguard and Fidelity, which most of us use because they're easy to use and have crazy low fees, have target retirement funds that will automatically allocate between bonds/stocks based on your retirement year. Or you could just pick a regular index fund like S&P500, Dow Jones, etc.
I'll probably have $1k at most to start out with and while I'll be adding as much as I can, the likelihood of hitting the max yearly contribution for a Roth is pretty much nil.