I step out onto slope (5)
'slope' is the definition.
(I have seen 'slippery slope' mean 'piste' so perhaps 'slope' could also mean 'piste')
'i step out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'istep' anagrammed gives 'PISTE'.
'onto' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for piste that I've seen before include "A ski run of compacted snow", "Skiing course", "Ski slope", "Skiing trail", "Ski-slope".)