use a slicer.

Did the printer come without a manual or start up guide ?
Usually they ship with an sd card with software and guides. The software that comes with them is generally bloody useless and called replicator-g.

The 2 free slicers are: makerware desktop and flashforge's flashprint

The best is simplify 3d - which isn't free but is worth buying.

Of the three I'd recommend you start with flashprint.