Having gas and having gas available to the engine are different things.
You think you have fuel so I would next check for spark.
Pull one of the sparkplug leads from the plug, insert any metallic rod-like object into the connector and position this so you have ~1" distance from any grounded metal on or around the engine.
Keeping free of rotating belts and pulleys, have someone turn the key as if to start the engine.
You should see within a few seconds, a fat blue spark arc from the rod/screwdriver to ground.
If you do, then you know you have spark.
If not, then a coil pack or coil may have failed and will need replacement.
The next step would be to locate the fuel line coming in from the rear of the van and check for a fuel filter; this will probably look like a cylinder with a flange around one end.
If it is plastic and clear enough, check for the presence of fuel
and any foreign matter.
If you see chunks or heavy discoloration, disconnect the hose from the incoming end of the filter and briefly, keeping face and any kind of fire away from the open hose, turn the ignition BRIEFLY on to see if gasoline is, in fact, coming from the tank.
If there is, change the filter and try to start the engine again.
If there isn't, the fuel pump or its fuse may have failed.
Check the fuse box to see if a fuse is labeled for the pump; if so, check it.
If it is OK, then the fuel pump (mostly located inside the gas tank), has likely failed.
Once you have found both spark and fuel, it gets tougher and you may need to have the computer scanned for error codes.
Depending on the make of vehicle, scanners can be bought for a few 10ers:
Scanner for OBD2
is one example.
Since we have . . . hmm 5-6-7 cars in our family, it gets exercised at least once monthly and has been a tremendous help.