On the Expression Atlas homepage you can search for genes and/or experimental conditions (Figure 1, Section 1). Start typing to see term suggestions from EFO and other resources (Figure 1, Section 2). Click 'Search Atlas' to submit your query.
Your results are shown in a heatmap, with a row for each gene and a column for each experimental condition (Figure 1, Section 3). Each heatmap cell shows in how many experiments the gene was found to be up- (red) or down-regulated (blue). Click on a gene name to see more information about the selected gene (Figure 1, Section 4) and on the heatmap cell to see more information about experiments (Figure 1, Section 5). Please see the full course on the Atlas for more details on searching.
Figure 1. How to search Expression Atlas.