If you want to be able to use your Sky+ box as before, and also watch Freesat on your TV, then you will actually need THREE cables from your Sky dish.
Terrestrial aerial cable goes into ANT1 on the TV.
2 of the satellite cables go into the Sky+ box as before. BUT, if you want to use the recording features you will still need to pay Sky. Full price as before for all the same channels you currently have, or ten pounds a month for the ability to record even the free channels. You should be aware the line of free channels is different on Sky than it is on Freesat as they are separate systems.
Third satellite cable goes into the ANT2(SAT) socket on your TV. When Sky installed your system chances are they probably installed what is known as a quad LNB that has four output sockets on it. If they did and you can get access easily to the dish, it's just a case of buying a length of new cable and the F Connectors, and cabling it up, running the new cable besides the existing ones down to the hole in the wall and passing it through to your TV. However, you might find that the hole in the wall isn't big enough for three cables, but you might get lucky. If the three cables are too thick you can either drill out the hole to make it larger, or you can replace all the cables with new thinner cables. Of course all of that assumes Sky installed a quad LNB, if they only installed a dual LNB then it can only take two feeds. You would also need to replace the LNB with a quad LNB, which is fiddly but not difficult. Normally it is just a case of disconnecting the existing two cables, releasing a locking pin, sliding the old LNB off the dish arm, sliding the new one on and replacing the locking pin.
If you aren't interested in recording but still want to be able to watch the free Sky channels on the box (you can cancel your Sky payments and your Sky box will revert to a Freesat From Sky receiver, although again bear in mind the channel line is different from actual Freesat), connect one cable to the first satellite input on the box and the second cable to the TV. Set the Sky box to single tuner mode (a quick Google search will tell you how to do that).
As you can see, it's a bit of a faff if you want both Freesat and still be able to record Sky channels too, as well as still having to pay something to Sky.