The first batch of TESS mission data is now available through MAST. This release includes all data from Sectors 1 and 2, observed between July 25 and September 20, 2018. This includes both FFI and 2-min cadence data.
The first release of the TESS instrument handbook is also available, as are data release notes. The details are on our documentation page.
For an overview of MAST services available for TESS, see their summary page. The TESS Archive Manual details data products, tutorials, and instructions on how to download them from MAST.