Understanding Spikeslab Output
BMA is "Bayesian Model Averaged". GNET is "Generalized Elastic Net". 

Have you tried reading the Ishwaran and Rao papers as mentioned in the documentation for spikeslab?  There's an article in the R Journal as well that might be worth reading too: https://journal.r-project.org/archive/2010-2/RJournal_2010-2_Ishwaran~et~al.pdf - no sense duplicating it all here.