First you have to decide if you want to invest at a bank or a broker. In most cases (at least for me), a broker will have lower fees than a bank but this is something you need to look at yourself as it depends on what country you're in.
But any bank, or broker, will most likely have access to index funds or ETFs. You can automatically deposit money in your brokerage (or bank account) and buy from there. Any automated investion options might be available depending on broker/bank (for example, automatically investing a monthly value in a certain fund / stock).
You will have to read up on the taxes in your specific country though, as this will impact the choice of funds or index ETFs. For example, I live in Belgium, and there is a 30% withholding tax on dividends, not taking into account the taxes from stocks from other countries. For example, if I hold a U.S. stock that pays a dividend, I first have to pay (e.g.) 15% taxes on that dividend to the U.S. (they are just deducted at the source), and then another 30% in Belgium. There's not much of that dividend left for me!
So, in this specific scenario, instead of buying ETFs or funds that distribute a dividend (called "distributing" shares or funds), it is much more interesting to buy those that reinvest the dividends at the source (called "accumulating") because I would lose about 40% when I would get that dividend and reinvest it myself.
Again, this is heavily dependent on the country you live in.
On top of that, not every fund or ETF will be available to you. When I started investing, I was very interested in some specific Vangaurd ETFs but they are no longer available in Europe to buy due to EU regulations. So, to conclude, I would say the following:
- Compare brokers and banks in your country (or even international). I went for a broker that only has fixed transaction fees when buying shares, whereas my bank would take a small % every year. The broker ended up being much cheaper (and there were a couple of 100 other reasons).
- Figure out your tax situation. For me, Belgium specifically, I figured I shouldn't invest in ETFs that were 'distributing' (gives me dividends), but focus on ETFs that don't distribute dividends and reinvest it themselves ('accumulating').
- After figuring out which types of Funds or ETFs (or shares?) you'd want to buy, go to your chosen bank or broker's platform and see if you actually have access to some of these products or not. There's no need to think about investing in a particular thing if it isn't available in your country or Europe to begin with. Perhaps some ETFs or Funds are available only at specific brokers or banks, and you might need to go back to #1.
That's about all the tips I can give you. You just have to figure out what kind of investor you are. I personally prefer lower management fees and I won't touch my investments for 40 years (i'm still young). This naturally led me to buying the same ETF monthly that tracks an index. In the future I will only buy every couple of months to even reduce the (very low) broker fees of buying ETFs, but that's pretty much it for me. I figured out this is the path I wanted to take before I invested in anything. Of course, this might all change in the future, as we all keep growing and changing as human beings.
Hope this helps you find your way.