English is simple. And it is the same in German. There is only one word we can use. However in Spanish there is a distinction. The difference between "por" y "para" is one of the things that don't come easy. But here are some simple rules.
POR
Use por, when you talk about
- Reason: Somthing happened because of something else
- For unspecific times during the day, like "in the morning"
- Approximate information of a place, like "the city center"
- The medium that is used. That could be the phone that is used to talk to someone, or the bridge that is used to cross the river.
PARA
Use the para, when you talk about
- If something is needed to achieve a goal. You need money in order to travel.
- If you are talking about specific dates and times when something needs to be done.
- If you talk about directions.
- If you talk about someone who receives some benefits.
