Jump across, initially moving right to left, to arrive at different levels (6)
I believe the answer is:
strata
'different levels' is the definition.
(plural of stratum - a stratum is a layer)
'jump across initially moving right to left' is the wordplay.
'jump' says the letters should be written in reverse (I've seen 'jumping' mean this (in a down clue, letters jump up)).
'initially' says to take the initial letters.
'moving right to left' becomes 'tarts' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'across' is 'a'.
'a'+'tarts'='atarts'
'atarts' in reverse letter order is 'STRATA'.
'to arrive at' acts as a link.
(Other definitions for strata that I've seen before include "Layers as of rocks in earth's crust" , "Beds of sedimentary rock" , "Geological layers" , "bands" , "Parallel layers" .)