ENVI version 5.4 opens Sentinel-2 data as 3 separate files based on their spatial resolution; 10m, 20m, and 60m. After opening the data and exploring it, you should save one or more of these datasets in the standard ENVI format to make data access quicker in the future. The YCEO Lab currently supports ENVI 5.4.1 and can be used to open all Sentinel 2 data.
First you will need to extract (unzip) these data using a tool such as 7-Zip. Data for the file will be placed in a new folder. From the ENVI version 5.4 main menu select File | Open. Navigate to the new folder and select the file MTD_MSIL1C.xml. ENVI will display the 10m resolution Color InfraRed view of the scene and the lower resolution (20m and 60m) files will be available in the Data Manager.
You can examine the data and if you wish to use these data in the future you are encouraged to save the file in ENVI format. From the ENVI main menu select File | Save As | ENVI Standard. Select the 10m file and save the output to a new folder structure for your project; it should not be placed in any of the original Sentinel folders. Consider including 10m as part of the filename to indicate the resolution.