He means, when you play a campaign in multi it 'whooshes' you along to the next mission, anyone who's stayed connected will get whooshed along with you.
There is no saves, and no medals in the campaigns, so you are better off playing them as singular missions.
Campaign support/enthusiasm for multi has been horrendous both from Volition and the HLP community, you wont get much joy there (it's buggy, and there's very little content for it).
You could convert some yourself, but they would require rebalancing to get much enjoyment out of them multiplayer.
I would suggest getting used to flying the singular FS2 Co-Op missions, or the dedicated multi missions, rather than trying to make a campaign file like the FS2 SP one, for multi..