Well this is directly from wowwiki:

This macro will on right click make a soulstone (change for appropriate level), left click, use it and on alt left click cast it on yourself.

#showtooltip Minor Soulstone
/cast [modifier:alt,target=player] Minor Soulstone; [button:1] Minor Soulstone; [button:2] Create Soulstone
Notice he uses a /cast for the soulstone, not a /use.