If the TV receiver itself is capable of directly resolving (aka capable of tuning to a frequency in a supported frequency range and what you want to tune into falls into that range, and also has a digital receiver equipped for DVB-C decoding, not just DVB-T decoding) - then direct 'reception' of the 'free to air' cable distributed programming is possible, as you probably have realised - that's entirelty down to the receiver, the DVB decoder, and what form of digital transmission is used.
So assuming you already have been able to view the digital 'free to air' stuff on cable, then the secure stuff (aka subscription and/or closed-group and/or non-public) that's sent using the DVB-C specification modulation and encoding simply needs a suitable DVB-C receiver and a decoder.
Since you have a 'DVB-C tuner', which really means you have a receiver with DVB-C demodulation and digital decoder capability (basic or otherwise), then what you generally would need is :-
a) A valid subscription to the service or services, or multiple subscriptions according.
b) A secondary decoder that decrypts the input 'encrypted' transmissions to present decrypted 'free to air' versions to the on-board DVB-C receiver in the TV.
On modern DVB capable TV receivers, which are pre-equipped for optional closed content (such as subscription viewing), then there is either a built on 'decoder' (or in reality, a decryption module) to handle the decryption process and the baseband or direct demux (roughly speaking, like it passes the equivalent to an 'open' demodulated content to the main DVB receiver module) - or it has a CI (Common Interface) socket or two.
A CI is a slot that you plug a decryption module into, and your subscription card is slotted into the decryption module - so that (as a looped through device) does the decryption for the DVB receiver module.
So a receiver that's 'equipped' already either has at least one decryption module fitted (there will be a card slot for it already present) or (in most cases) has the CI facility.
So given that the CI facility removes the need for an in-line external decoder/decrypter/receiver (or any two of those functions integrated) - you need to discover what is fitted.
Then, obtain the correct components - aka if a CI slot needs a decryption module (called a CAM) for a particular type of decryption used by a service, then you need to obtain an example of such a CAM/Decryption module. You will also require a smartcard (in most cases) which is (whilst it is live, and valid - aka not crippled or disabled by service provider) your 'passcard' that is inserted into the CAM and provides authentication for decryption of the service in question.
As for sourcing these, contact your regions's available service providers (these will include coverage of national services available as well as for the area/region specific services). For stuff that is carried, but not destined for the area (aka it's just being distributed over cable under some agreement, as a hubbed link - destined for adjacent region or distant region use) - you'll probably not be able to by legit authorised subscriber access cards without a foreign sourced purchase since the content is probably not destined for your area. Cams can be purchased, even ones for other encryption types for anywhere in the world practially, separately - but they are pretty much paperweights without a valid subscription.
So for legal, authorised viewing - contact the service provider for the services in question, where they will supply (for a subscription fee and/or deposit) a subscriber access card and/or cam module to allow the legal, authorised viewing - you may or may not be required to use an external receiver/decoder/decryption set-top-box, according to what the service provider issues.
For non-authorised (aka out of region encrypted viewing, non-'free' services) you'll have to hit the search engines and find your own info, since i don't support willingly or otherwise, efforts to break encryptions (aka bypass security) and access content that's not authorised for your usage.
Providing the info, sources of info, in the respect of how to 'bypass' or avoid cost of subscription would be effectively telling you how to 'hack' the broadcasts for viewing, which would be in part against the rules of Y!A, at best, and also make me party to helping you bypass such security.
Sorry if that's not, in part or whole, what you wanted to hear/see.