You can mix it with your powder but you need to watch the ratio of glitter to powder.
If you are only still in your training you maybe need to get to grips with the mix ratio of liquid to powder first, before you move onto glitter.
What products are you training with, as there may be a range of premixed glitter powders available from their system and then you know you won't have any problems.
EzFlow and Young Nails and NSI have some great glitter and coloured powders.