Try reading company annual and quarterly reports to help decide if you want to invest in their stock or not. These reports contain a wealth of information including candid management discussions, financial sheets, disclosures and much more. These are long documents that do take time to read but my side project (shameless plug) https://www.Last10K.com aims to help investors read these documents more efficiently.
You can also google study materials for the Securities Industry Essentials (SIE) exam which covers basic securities information that can be applied to investing.
https://www.finra.org/registration-exams-ce/qualification-ex...