fay, if you start with knowing nothing about diesel engines, it might be worthwhile to try finding a competent diesel mechanic
(try) and pay them to come down and spend an hour showing you what to do with the engine and fuel system.
Some fuel systems use crush washers, paper-thin copper washers that deform to seal fuel lines. If your engine does, and you loosen one of those connections to bleed it and then just tighten it up again? Uh-uh, the crush washers are like kleenex, used once and then MUST be replaced or you'll wind
up with air leaks
and fuel problems. If you engine uses them, buy a box full, the shipping
costs more than the washers do.
If your engine has decompression levers, you can open those up and then usually turn over any engine by hand, turning the flywheel, or putting a wrench on it. If the rings have not frozen up, you can do this. If they have frozen up--that's when the mechanic
starts earning his pay.
If you can also download or buy a manual for the engine, it may also detail operations and maintenance
and give you a chance to see what is involved. Diesels are very reliable IF the fuel supply is kept pristine. IF there are no air/fuel leaks, IF there is no water or crud contamination. But when they do throw a tantrum, it is often a very good one.