Most wood floors are now supplied pre-finished rather than to be finished in situ as used to be the case. This means that they will arrive with a suitable wood floor finish prior already applied. Generally these are fully finished, ready to walk on the day that they are laid and do not require any additional finishing. However, this is not always the case:
Some pre-finished floors require further finishing after installation - most commonly these are oil finishes but can be the case with other finishes too. Increasingly you will see these floors described as part or semi finished (this is certainly the case at Broadleaf) but this is not always the case by any means so it is worth double checking before you buy if it is not made clear in the product description.
Wood floors pre-finished with Hardwax Oil have a natural look and offer good durability with relatively low maintenance. They can be easily refurbished if required without the need for the original finish to be sanded back (unless this has worn so far that the colour has become patchy).
Oiled wood floors are less durable and will normally need regular treatment with maintenance oil to keep them looking good.
Lacquered wood floors (the professional term for varnish) offer good durability and low maintenance but they do generally have a more processed look and will normally need to be sanded back to bare wood before they can be refurbished.
However your wood floor is finished, use the recommended cleaning products to keep it looking its best. Avoid generic floor cleaning products from supermarkets, which often contain harsh alkalis which can damage floor finishes over time and make them less resistant to dirt and wear, and whatever you do DO NOT steam clean your wood floor.