SessionExprBase
After you create a new session using the "Expression data loading" selection, then the following page shows the steps which are possible for getting the expression data ready.
The first step is highlighted blue. After you complete each step, then the next step is highlighted. (NOTE: this doesn't always work since not all steps are required, and sometimes you want to go back and repeat something... so the blue highlight is a suggestion, not a requirement). In this case, you just created a new session, so the next step is in fact the first step, which is to upload the data:
After you click the blue highlighted step, you will see a page where you can upload 4 files. Each file has a brief description and a link to an example file. The 4th file (score metadata) is optional at first since you can generate this file using the analysis in the app.
Please read the wiki page on Registered Files to learn a lot more about how to format the files before uploading them.
Now that your 3 main files are uploaded, you can proceed to manipulate, analyze, perform calculations and load the expression data.