A. The New York subway system is huge and we admit somewhat complicated. However, you can get to most parts of the city quite easily by just following simple directions.
You can get detailed directions to where you want to go on smart phone apps or online. You can also just ask a ticket agent.
If you are old enough to be getting Medicare, you can show your Medicare card and get a 2-trip discount when you buy tickets.
Otherwise, there are other ways of buying tickets or a MetroCard ®:
New York City Subways and Bus Fares > http://web.mta.info/fares/
The NY Transit Authority website has tons of information and maps about how to use the transit system.
New York also has a comprehensive bus system and if you want to see more of the city you might elect to travel by bus. But bear in mind that the buses are going to be a lot slower, especially during rush hours, when they are not at all advisable.
The subway system is very safe and even late at night is full of people.