Simple bed levelling and adhesion test. It's 15x15cm, 1mm height square. With proper skirt (you can set in slic3r distance from object) you can check virtually any bed size.

How to level bed (few steps) (i3 prusa and other frame constructions)

• check levelling of the surface you keep your printer on (if it's not completely level - remember that the same difference you should see on printer)
• check level of your Z axis frame - it should be the same, as the level of surface you keep your printer on. Keep in mind, that if you have two Z axis stepper motors they are not connected, you can simply twist one up/down to level Z axis arm.
• set all bed levelling screws on the same level, somewhere in 2/3 of it's height
• adjust Z axis stop, as close as you can, to current bed level
• set all 4 (or 3 - depends on model) bed leveling screws to height when nozzle is touching bed but you can still push under it a piece of paper
• after you set everything up, home extruder again and repeat check nozzle distance in all 4 (or 3) corners of bed (with a piece of paper)

Finally, you can tune first layer height and first layer extrusion in slicing program - so it will stick properly to surface.