Biogas is produced from decomposition of organic matter, usually in a digester of some sort. It is a literal gas, primarily methane and CO2. Think propane substitute.
Biodiesel is refined via chemical reaction from veg oil; methanol+lye are combined to make 'methoxide', which is mixed with the veg oil in a reactor; this then separates into biodiesel, glycerin, and some other minor byproducts.
It is a liquid fuel, compatible with pretty well all applications where diesel is used.
Too long, but that's what I've got right now..
'Theoretically this level of creeping Orwellian dynamics should ramp up our awareness, but what happens instead is that each alert becomes less and less effective because we're incredibly stupid.' - Jerry Holkins