The eCannon is a starter ball machine for groundstroke and volley practice. It throws all balls with topspin (like all one-wheel tennis machines) and therefore is not recommended for beginners.
Just choose Level 1, 2 or 3 (Level 1 is slowest) on the control panel and push the power switch on. The eCannon sets the ball speed, ball trajectory, and interval between shots appropriate for a groundstroke at that setting.