[R] R questions

[Lynda]

 I have a few questions for R:

1. Other than using a built-in function such as mean(), how do I know if 
it is installed in my current version of R?

2. To get help in R, I can use several ways:
?sort
help.search("sort")
help(sort)
apropos("sort")
the help menu

are there any other ways to get help?

3. When I see a help menu for a function, does it mean the function is 
installed?

4. If I execute a program file that contains output files that doesn't 
have a path specified, which path is it going to output to? Is it the 
Current Working Directory that the output file is going to output? if I 
change the working directory by using setwd(), is that going to change 
where the output file path permanently until I specify it again?

Thanks a lot!
Lynda