If you're getting started, chose a fund like a target
date fund,
retirement date fund, they go by a couple of names but you can start with just one mutual fund that's a collection of all the investments that might be appropriate for your goal and from that core, if you want to then start branching out into
specific ETF's or funds that focus
on just one index or individual securities, then you've got that base that you can build
on to add those things in but at the very beginning, keep it simple.