Hello, what have you tried so far? In a nutshell (Basically), you must do this:
- use the filters at the Data Portal to select the files that you want to download
- download the file manifest
- use GDC Data Transfer Tool with the file manifest to download the files
If this process is too difficult, then use a package like TCGAbiolinks to download the data for you. It is a comprehensive package that covers the needs of the most basic TCGA users.