It's a basic general coverage receiver which was popular in its day, like all Codar equipment. From your picture it looks in pristine condition and you bought it as a bargain price. If it needs any attention, (eg, reservoir/smoothing capacitors and V3 cathode bypass capacitor) it's easy to work on. It has a Beat Frequency Oscillator ('BFO'), so can resolve SSB and CW (Morse) radio amateur transmissions from 160 Metres to 10 Metres (if there are any to be heard these days).
It needs an external aerial to work.
One fault which can result in a dead set is if the OA81 germanium detector diode fails.
If that fault did arise, a IN34A widely and cheaply available if you can't source and OA81 would be a suitable substitute.
You can download the user manual here including the circuit from this link:
http://www.g4kfk.co.uk/Codar_CR-70A_Manual.pdf
Hope that helps a bit and that you get pleasure from owning and using it.