Pull apart your pallets and discard any components you won't be using, including old fixings. You need 8 long timber slat lengths and 4 short timber lengths (to be used as vertical supports).
Decide on size of raised vegie garden, using long timber slat lengths as a guide. Drive a vertical support into the ground at each corner (you can use garden stakes for this, if you wish). Vertical supports or stakes should stand three slat-widths above ground level.
Screw or nail long slats to verticals on all four sides. Leave a gap, then screw or nail four more long slats, flush with top of verticals. Keep all slats level using spirit level.
Line the vegie garden frame with weedmat. Trim weedmat to fit, if necessary, then staple it close to the top edge of the top slats on all four sides.
Fill the vegie garden frame with suitable potting mix, then get set to plant up!
Start with one raised vegie garden, then expand your crop capabilities by adding more beds as you see fit. You can replace verticals and slats as they deteriorate over time, as required.