Stand the central rod in the base, then stack each part one by one, shifting them as you go.
Literal
Base [on-に] core-rod [object-を] stand-[and-て], each part [object-を] shift-[while-ながら] stack-[continuing-ていく][polite-ます].
An assembly or craft instruction. ~て links the two sequential actions (stand the rod, then stack). ~ながら on ずらす marks simultaneous action — 'while shifting.' ~ていく on 重ねる gives the stacking a forward-progressing sense: the action continues to unfold step by step. 心棒 ('core rod, spindle') and 台座 ('pedestal, base') are on the technical side.