Were there no connectors on the ends of the cables when you first saw them? Just bare copper braiding and a copper core surrounded by plastic? I can't imagine why they would be like that, there's no reason for the former owner to rip them off, unless for some reason he couldn't manage to unscrew the connectors from his Sky+ box and decided to just cut the cable instead.
If you have had to replace the connectors, firstly a stupid question, but did you use the correct f-plug connectors, i.e. one of these:
and not a standard terrestrial aerial connector? If you try to use a standard connector you won't be able to mate it with the socket on the back of your Freesat box properly.
If you have got yourself the proper f-plugs, then fixing them on the end of the cable isn't too difficult, it's a case of stripping back some of the sheath and screwing the thing on (unless you bought crimped connectors, in which case you need a crimping tool as well). The most important thing is to make sure none of the copper braiding comes into contact with the solid copper core of the cable.
Once you have your f-plug in place, it should fit snugly over the socket on the back of the Freesat box, and then you need to screw its small nut into place to tighten the thing up. Finger tight is enough.