Search the forums - this comes up regularly.
The short answer is that OFP is not very good at this. If you have a convoy of vehicles of all the same type (i.e. all tracked or all wheeled) it's fairly easy. Make all the drivers in the same group, put waypoints on the road (use as few as possible) and set the behaviour to safe and formation to column. The front vehicle is driven by number 1 in the group (usually but not always the senior soldier), the second one by number 2 and so on.
For a mixed group, whether different types of vehicles or vehicles and walking loons, the short answer is don't bother, it's probably not worth the trouble. If your mission depends on it, then you need a following script. I'm not sure if there is is one in the Ed Depot ... you might find a link if you search the forums. Alternatively go to
my website and d/l my beta mission Regina Proeliorum. It has a following script (it's called Shilka1.sqs) which you could adapt for your own mission ... obviously I'd appreciate a mention if you do.
The custom formations script I've never used so I don't know if it helps here. However, I doubt it.