What The??

I drove to work and parked my kombi in the carpark and headed off for a 12hour shift in Intensive Care... After an absolute shocker of a shift I returned to the van, turned it over and it wouldnt run/idle. It sounded odd but wouldnt keep running. Now I keep it running really well and never have any problems with the engine.
I took a look in the back but I couldnt keep it idyling- anyway it had oil and wasnt leaking anything onto the ground.
So I very carefully drove home.. slowly.. tried to avoid all the traffic lights I could and got it home.. very depressed thinking that I had major troubles. I thought I might have got a bad batch of fuel because the tank level was low but I put another $10 of fuel in and it didnt help.
I got it home and and called RACQ to get them to tow it to my mechanic- Phoenix Engineering- the next morning but instead we decided to get a mobile mechaninc to have a look before we booked the tow. He had a look while I pumped the pedal and within about 40 seconds had put a hose back on and she was back to its glorious self..
Something to do with a vacuum on the carbies?? What are these?
What do they do?
And how/why did it come off?
Is it supposed to fit on tightly or does it suck on once the engine is going?
I didnt hear it backfire when I started it but then I ALWAYS have the stereo cranking and rarely hear anything anyway

Depending on the year, model, mods made over the years, etc you may have several or no vacuum connections. On my 76 kombi there are 2, one drives the vacuum advance on the distributor, the other provides the vacuum for the power assisted brakes. If you have a vacuum leak, more air is getting into the manifold weakening the air/fuel mixture and making the engine run poorly. The problem is compounded if the leak is the result of the hose to the distributor falling off because you wont get full advance. The hoses should be a tight fit. I can't remember if mine are clamped or not. I think it's one of each!

Well thanks! It was definitely affecting my brakes so that must be it. I have a 2 ltr 1977 Kombi automatic with standard setup... I think