ESRI has created hundreds of web courses and other training materials to help you learn ArcGIS and other ESRI products. ESRI web courses are:
If you are a member of the MIT Community, create an ArcGIS Online account and then you can use that login for ESRI training. Ask if you need suggestions for courses!
**Note that some training materials are not available for free, such as in-person training, certification prep, books, etc.