How do I output an individual?

You can use the Individual's toString() method:

std::cout << individual->toString();

Alternatively, you can use the Individual's write method for output to XMLNode, then convert XML to string:

XMLNode xInd; 
char *s = xInd.createXMLString(); 
logger->log(1, "Individual: \n" + std::string(s)); 
// or just output with std::cout
freeXMLString(s);	// NOTE: XMLNode::createXMLString requires manual deletion!

How do I log things?

Use the predefined ECF_LOG macro; it requires a pointer to State object, log level and string message, e.g.:

ECF_LOG(state, 1, "message: " + uint2str(4) + dlb2str(3.14));

Level 1 is the highest (always logs), all the other (up to 5) depend on the "log.level" parameter (the default is 3).

How do I make something happen each generation?

Write and add a minimal operator (for more complex ones, see Adding the components) that does... something, e.g.:

class MyOp : public Operator
        bool operate(StateP state)
                std::cout << state->getRandomizer()->getRandomDouble() << std::endl;
                return true;
typedef boost::shared_ptr<MyOp> MyOpP;

and add it to State before State::initialize():

MyOpP myOp = (MyOpP) new MyOp;

How do I access population, hall of fame, statistics...?

All of those are available through the (local) copy of StateP pointer:

state->getPopulation();       // population (vector of demes)
state->getStats();            // population statistics
state->getHoF();              // population hall of fame
state->getAlgorithm();        // current algorithm
state->getIndividualObject(); // initialized individual
state->getFitnessObject();    // initialized fitness object
state->getGenerationNo();     // current generation
state->getGenotypes();        // current genotypes (vector)
state->getRegistry();         // parameter repository
state->getRandomizer();       // current randomizer
state->getTerminateCond();    // is evolution terminating
state->getElapsedTime();      // since start, in seconds
state->getCommunicator();     // communicator (parallel ECF)