You can find a detailed explanation of all the functionalities available at http://rest.ensembl.org/. This includes all the interfaces and Python code snippets, among other languages.
If you are interested in paralogues, this information can be retrieved quite trivially from the preceding recipe. On the call to homology/id, just replace the type with paralogues.
If you have heard of Ensembl, you have probably heard of an alternative service from UCSC: the Genome Browser (http://genome.ucsc.edu/). From the perspective of the user interface, they are on the same level. From a programmatic perspective, Ensembl is probably more mature. Access to NCBI Entrez databases was covered in the previous chapter, Chapter 2, Next Generation ...
