Fold change vales are the ratios of the average normalized expression values between experimental and control groups for each gene in the dataset.
Fold change values greater than one indicate up-regulation in experimental groups relative to control groups. Fold change values less than one indicate down-regulation in experimental groups relative to control groups.
As easy as these calculations are to perform, the RNA-seq Analysis Portal automatically calculates them for you, once you set up your RNA sequencing based differential gene expression analysis by defining the samples and groups to be compared.