If you are in Europe, Interactive Brokers is the most well-known and seemingly well established platform. I am still exploring it myself, but it has low purchasing fees and a lot of learning material to start from.
The specifics depend on the country you’re in. In the UK for example there’s a type of investment account (ISA) in which you don’t have to pay tax on any income from capital gains or dividends. There are also private pensions that have other tax benefits but require you to lock your money until a certain age. Both of these might be preferable to a general investment account. Similar tax-advantaged accounts might be available in your country. And then there’s the choice of actual platform, and that also varies by country.
Be cautious with banks having crazy transaction fees for generic stock. Most of them have own funds and you can purchase them for low fees, while the rest can be even at 15 EUR per single transaction.
That's exactly what I noticed with my bank. They have high fees for investing and for withdrawing. And that's an issue for me since I would only invest a few thousand dollars every month whenever I get my salary paid... Perhaps I should compare the fees of all the local banks next.