General investing or individual stock purchasing?
You really don't need to dig too deep if you are just investing for retirement. In fact don't nuke it. Read the forum on index investing. A combo of VTSAX and VBTLX will do just fine. Adjust according to your volatility tolerance (how fast you can tolerate temporarily losing money), because it will go up and down. Up more times than down over years. The shorter the time the harder to tell. Then make it a point not to look at it for a long time. Its better that way.
By the way, Im summarizing what 80% of the forum will tell you. I take a different approach.