I'll avoid the high/low terms as they are often a source of confusion.

You set the smallest cog limit with the cable slack, disconnected if you like. Then tighen the cable to remove all he slack but not enough to actually cause the cage to move off the stop. Now set the largest cog limit by manually pulling the cable with your hand. This is easiest to do by yanking the cable sideways between two of the cable stops. Once you've got the two limits set, then fine tune cable tension to get proper indexing. Final step is b-tension - shift to largest cog and adjust to get good spacing between top jockey wheel and cog.

Hope this helps.

- Mark