Please don't hit me too hard, but exactly what are these index funds I keep hearing about, what sort of related fees do I need to plan for, and how much do I need to get started anyways.
There are lots of articles on this, so google-away as another poster suggested to get more info.
Here's a quick summary to start.
An "index" is basically something that tracks an entire segment of the stock market. There are standard criteria that are used to put these stocks into the index and the percentage of these stocks. The most common index you'll hear about is called the "S&P 500", which are the largest 500 publicly listed US companies. The "S&P 500 index" are a collection of these stocks, weighted by the value of each stock (eg. a stock worth 2 billion will be 2x as large a portion of the index as a stock worth 1 billion). There are other indexes that track other stocks including European, Australia, emerging markets.
An "index fund" is a fund that tracks an index. So when you buy $10,000 of an S&P 500 index fund, you are buying some proportion of the 500 US stocks in the S&P 500 index. Because they don't require active stock picking, they generally have low fees (check this before buying). Because the general stock market goes up in the long-term, you will effectively be buying the general upward trend of the stock market if you buy and hold for a long period of time. The S&P 500 has historically had a 10% annual return (6% after adjusting for inflation), although it fluctuates dramatically from year to year ("volatility").
In truth, an index fund is simply a very special mutual fund, although when people talk about "mutual funds" they are usually talking about funds that have a manager who actively picks stocks that they think will do well. The problem with mutual funds is that the fees are much higher. The managers don't always pick stocks that do well and even if they happen to pick better stocks, the fees are higher than the improvement in the returns. On average, actively managed mutual funds do worse than index funds for this reason. This is why many people, including many on this forum, advocate for holding index funds.
If you have a reasonable amount to invest (at least $10,000-$25,000), then you can also buy ETF's (exchange-traded funds), which can also track indexes, so as you are doing your reading, you can google that as well!