Gary Hinson ZL2iFB, has published a wonderfully complete FT8 operating guide.  You can get a copy at the link below:

http://www.g4ifb.com/FT8_Hinson_tips_for_HF_DXers.pdf

And of course the WSJT-X program, which is what is required for FT8 operation can be found here:  https://physics.princeton.edu/pulsar/k1jt/wsjtx.html