[R] about p value

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Hello sir:
I am a data analysist of a bio-company.
Here's a question about microarray for identifying the differentially expressed genes.Thanks for your help.
First,I wanna make sure whether I've grasped the difference between the"unadjusted p-value" and "adjusted p-value".
 
1.Unadjusted p-value,which is calculated from t-statistic(just call it "t0").e.g if t=1.96,then p=0.05.
 
2.Adjusted p-value.p-value here is FDR(Falsely Discovery Rate) ,and it's different from the unadjusted p-value which is calculated according to the t0.In the permutation(say 100 permutations)of a gene,there will be 100 t values in total.If there are 20 t values whose absolute values are greater than t0,then the adjusted p-value=20/100=0.2.
 
Is that right?
 
And how can we define which genes are differentially expressed?
By t0(|t0|>1.96 is significant in 95% significant level) or by adjusted p-value,which needs us to set a cutoff of FDR?
 
 
Thanks a lot!
 
Best regards!