Short-term visas are also called “Schengen-Visa” as they allow a stay up to 90 days in a 180-day timeframe in the Schengen area. A short-term visa is needed for any stay shorter than 90 days.
If you intend to stay longer than 90 days, you would have to apply for a long-term visa (also called “national visa”).
You can check here if you have to apply for a visa to travel to Germany.
You can check here if you need an Airport Transit visa.
You can check here if you need a visa if you have an Irish travel document.