Baby me on investing pls

I have some cash that I would like to invest, high five figures.

I appreciate that there are a million choices and everyone will have a view as to that, but I am fairly comfortable that I want an S&P500 index (regardless of recent turmoil) and really have 2 specific questions for the inimical TZ hivemind, as I’m new to this:

1. What’s the best way to do this tax efficiently (I have no tax structures around any assets currently); and

2. What’s the “best” (I suppose that means a combination of high value and high safety) platform through which to invest? (Or is there sense in splitting across >1 platform)?

Many thanks!