lea edx, [esp+24] - load effective address edx as esp + 24 ... look upon this as pointing to an array
mov eax, [esp+140] ; load some pointer to an address .. look upon this as the index
add eax, ebx ; pretty much index + base..
movzx eax, byte ptr [eax] ; load value from the area
the movzx part could have been written as
movzx eax, byte ptr [eax+ebx]
same thing essentially, just removing the add eax, ebx (which is probably there as there'll be some reuse or whatnot later)