There are books and courses on various strategies, but I didn't use any as it started as a hobby and trying out different approaches & finding "hacks" on my own was more fun (it turns out all of these "hacks" were known previously, who would have thought).
If you have purely technical questions, reddit has a few communities that can help and you can find more people on Discord.
Understanding stocks, options and all the financial stuff was the hardest part (for me as a non-fintech guy) as it's filled with their own lingo and large part of information available online is useless or even harmful (either coming from noobs/gamblers or "financial gurus willing to disclose their secrets for in a private webinar" or even legitimate traders that operate through textbook "cargo cult" rituals). Investopedia is a good start, but if your goal is to have profitable algorithm that does not require your attention, you will need to read and understand the rules and regulations that apply to your jurisdiction and exchanges you use. There are many somewhat obscure events that happen fairly rarely (during normal times - low volatility period, right now everything is accelerated 5x) so you might not hear about them at all until they affect you, but once they do occur you will either lose money or lose opportunity. I am going for sources (sec.gov, nasdaq.com, nyse.com - I trade US options exclusively), there might be some shortcuts (probably trainings), but I haven't tried any.
If you are just starting, try paper trading but also get a real account with real money as soon as you can (If you want to be above the average algotrader - start by collecting detailed data (per minute or so) and storing it for future use. Many brokers give you access to historical data but it is very basic and good quality historical data is very expensive. Use this dataset to backtest your algorithms, but try to make distinction between features that have real-world causes, the ones that are just product of chance and the ones that are caused by market makers or other traders. Most of the trades are happening fully automatically and everybody uses basically the same few sets of approaches, so you should be aware of them to either make or avoid losing money on those somewhat predictable components.
Oh, also make sure you understand the way your broker calculates all the fees and commissions as with algotrading that can make or break the whole profitability for you.