Quick example NEW LDIM FROM /item1 TO /item2
will create basic dimension of default East horizontal direction between /item1 and /item2 (by their name) (having in mid that your drawing has North plan=Down direction)
If you need the same but in vertical (for same driction of view) then NEW LDIM DIR N FROM /item3 TO /item4
The same you can do attaching to points like NEW LDIM DIR N FROM P1 OF /item3 TO P2 OF /item4
