1. Installing a package is very straightforward, and is like the normal npm installation:

npm install <package>

2. The most important directories in a Truffle package are the ./contracts and ./build directories.

3. To import a package into your contract, use Solidity's import statement. Specify the downloaded package name and the filename to import it:

import "npm-library/contracts/contract.sol";

4. To interact with the contracts from JavaScript, refer to the package's build files. Using them with truffle-contract will convert them into their respective contract abstractions:

var contract = require("truffle-contract"); 
]var data = require("npm-library/build/contracts/contract.json"); 

var SimpleNameRegistry = contract(data);