Step 1:
Forget about the DVD recorder altogether for the moment. Instead, connect the aerial to the Freeview box and the box to the telly (probably via a Scart lead but that will depend upon which connections you've got available). Use the TV's remote control to set the source to 'Scart' (or whatever the Freeview box is connected to). Check that you can see a picture from the Freeview box and that you can change channels with that box's remote control (rather than with the one for the telly).
Once you've done that you'll have no doubts about whether the set-top box is outputting a suitable signal or not. You'll also know that your telly is accepting a signal from an external device. So . . .
Step 2(a): Put the DVD recorder in between the two existing devices. You'll need to use the three-coloured phono input sockets on either the back or the front of the DVD recorder to accept the output from the Freeview box. So you'll either need a phono-to-phono lead (if your Freeview box has got similar sockets available for its output) or a Scart-to-phono lead (if your Freeview box only has a Scart output). NB: If you're using the rear sockets on the DVD recorder, ensure that you use the ones labelled 'Input'; they're at the top right.
Step 2(b): Complete the line-up by connecting the output of the DVD recorder to the input of the telly (preferably using the same input as you've just used with the set-top box, so that you'll know the TV already has the correct source set).
Step 3: Use the DVD recorder's remote control to select the appropriate input source. Press 'AV/Input' until 'AV1' is shown if you're using the connections on the rear panel but select 'AV2' instead if you're using the front panel connections.
You should then be able to see the output from your Freeview box and to record it, simply by pressing the 'Record' button. [NB: Your DVD recorder doesn't offer a 'timed recording' feature when using an external device, such as a Freeview box, to provide the signal. You have to manually start and stop the recording yourself].
With just that set-up you can only record the channel you're actually watching. To enable you to watch a different channel at the same time you'll need to connect a fly lead from the 'AE Out' (or 'RF loopthrough') aerial connector on the Freeview box to the aerial input on your telly. Then you first set everything up as above to start the recording. Once that's done, you can change the 'Source' setting on your telly, so that you can watch a different channel while the other channel continues to be recorded.