Unless you buy a DVD recorder with a Freesat tuner built into it, you've only got one Freesat tuner in your system. That means that you won't be able to watch one channel while recording another. (That requires two tuners).
However if you use a Scart lead to connect the output of the Freesat box to the input of the DVD recorder, you'll be able to record Freesat channels. (You should connect the output of the DVD recorder to the input of the TV in the usual way).
Since channel selection will be via the Freesat box, and not via the recorder, your DVD recorder should be set to record the signal from an external device, rather than from any numberer channel. The label on the button which you need to press varies between manufacturers. It's likely to be labelled 'AV' (or 'AV1' or 'AV2') but it might be shown as 'Line In', 'Line', 'Ext', 'Aux' 'In', 'Input' or something else!
Chris