You have literally no experience with banking and investing, so you should let someone else handle the actual trading.
Many banks have investment funds targeted at specific areas (sustainable development, microloans), or avoiding areas (nuclear, weapons, fossil fuels, etc.)
Assuming you have consumer organisations or independent investigators in your country*, find the reviews that they publish about sustainability of banks. Pick those that come out best, then examine the funds they offer, and invest your money in one of those.
One additional benefit of choosing an 'ordinary' bank (instead of e.g. private investment funds) is that they are likely more stable, with a more reliable return on investment. They also have people overseeing them.
* (You may want to add that to your question)