If you want this to be a working fireplace you will need to first have it inspected and swept by a chimney sweep. The chimney sweep can do a smoke test to check for issues such as leakage and blockages. This involves setting off a small smoke pellet and looking to see if smoke comes out the chimney at the top, and anywhere else it shouldn't be.
At his point you may find that the inside of the chimney has issues such as being blocked up, or even be at risk of internal collapse. If the pointing is in poor shape this could let gasses through into rooms which are passed by the chimney. The inside may have become rough which will reduce the flow of air up the chimney due to friction. The usual solution to these issues is to fit a flue liner which will offer some support. These can be flexible and fitted by shoving (to use the technical term) them down the chimney from the top.
Be warned though that this can be easier said than done. In my circa 1830 house the flue has bends and a few holes (small, about 500mm square) had to knocked in walls to get access and clear blockages.
If you do require a flue, in the UK it must be fitted by a HETAS registered installer. An incorrectly fitted flue and fireplace can lead to carbon monoxide poisoning.