This is a scale from 1 to 10, with 10 being an all-out-maximum effort (e.g. sprints) to 1 being a minimal effort (e.g. walking). 

Descriptions next to RPE rating indicate how you should be feeling during that level of exertion.  This is a subjective assessment on your part, so don't worry about getting it exactly right - you will become more familiar with the rating as your training progresses.