Student or Learner
Erect the wood skid on a ground level sufficiently able to take the maximum load.
I suspect that the sentence should read something like "Erect the wood skid on ground which is level, and is strong enough to take the maximum load".
I hope that makes the meaning clear. The wood skid must be built where the ground is not sloping, and where both the surface and the ground below are hard enough to bear the weight of the wood skid and the heaviest weight of material that may ever be placed in it.
Note that I take no responsibility, should you erect the wood skid [whatever that is] and it falls over, or sinks into the ground!
I'm not a teacher of English, but I have spoken it for (almost) all of my life....