Evaluation Measure
The evaluation is based upon the correlation coefficient between the predictions and the target values.  It has a value in [-1,1].  You are targeting a value close to one which means the predictions and target are highly linearly correlated.  A value close to zero indicates bad predictions and a correlation coefficient close to -1 means you should change the sign of predictions.
Submission Format
The sample.csv contains a sample submission file.  It is comma separated file, with first column being the id of the test set instance an the second one is your prediction on that instance.
Id,Value
1,1
2,8
3,9.7