Q:

R: How do I make my package use another package?

This is very simple question. 
I am extending someone's package. It currently uses packages A, B and they are listed in the DESCRIPTION file.
If I need functions from package C - to add a package to the dependencies - do I just add the package in the DESCRIPTION file and that is all that is needed? Into what section - Depends or Imports? Are there more other steps to make? Do I need to use prefix C::functionInC() once my code needs to use a package C function?

A:

Short answer:
Add C to Imports: and when using the C functions, use the double semicolon prefix.
Longer context:
The link below provides the following advice
http://r-pkgs.had.co.nz/namespace.html#imports
R functions
If you are using just a few functions from another package, my recommendation is to note the package name in the Imports: field of the DESCRIPTION file and call the function(s) explicitly using ::, e.g., pkg::fun().
If you are using functions repeatedly, you can avoid :: by importing the function with @importFrom pgk fun. This also has a small performance benefit, because :: adds approximately 5 µs to function evaluation time.
Alternatively, if you are repeatedly using many functions from another package, you can import all of them using @import package. This is the least recommended solution because it makes your code harder to read (you can’t tell where a function is coming from), and if you @import many packages, it increases the chance of conflicting function names.

