What is the different between pre trail and trial?

i worked at kohl's for over 6 months and few months ago the LP accused me that i have helped an outsider for company loss. because i have purchases few items with $10 off coupons and i told my parents to return the items if they don't like. so the next day my dad went to return the item and he got $10 merchandise credit. i live with my family, therefore whenever i need anything i get it from them. so i got the merchendise and purchased the items they like and i like. but due to this situation they accused that i was helping an outsider. they won't accept the fact that he was my dad. i had to go through all the legal action because of that. i had 2 pretrail and having a trial this month. so i was wondering what is the different between pre trial and trial. i also talked to few managers from different kohl's and ask them about my situations and they told me i have not done anything wrong. my parents are allow to return the items i purchased. as long as the person has my receipt anyone can return my items which i have purchased. and i also checked my contract with kohl's and the only thing they said that i wont able to share my discount with anyone not even with my parents but other then that they never mentioned anything like this that i can not use anything which belongs to my parents. how do i prove this to judge. i think i will be having jury in my trial. is it a good thing? am i going to have a chance to talk to judge or juries to explain my situations?