So firstly we need to address your concerning lack of residents. Although popular history often conceives of a largely empty medieval landscape, this was rarely the case. By the 1080s, the Domesday Book gives us a fairly extensive picture of land use in England, and what it shows us is that, broadly speaking, if there was viable land, somebody was living there and farming it. This doesn't mean that all land was in use at all times, but that broadly speaking, even land not being actively used for agriculture or forestry was included within the bounds of a certain estate or territory. Even in areas of low population density - The Peak District for example - settlements are still found in roughly the same distribution patterns as elsewhere, they just tend to be smaller. Gifts of land also tend to bequeath the villages and tenants therein; this is common not only in charters but in wills. The 10th century will of a Wynflæd leaves her daughter not only two estates, but also all of the people, houses and resources therein, apart from the freemen. So if you've been gifted empty and unused land, your first thought might be "Where have all my peasants gone?!"

The other option is that you're involved in seizing territory on a frontier somewhere. I'll focus on the Anglo-Norman Welsh marches of the 11th - 13th centuries, but the situation is roughly similar whether you're in 12th century Ireland, 10th century Germany or any other frontier. As R.R. Davies states, claiming land in a frontier region was more often a 'statement of intent' than a de facto control, and had to be enforced via 'strenuous military efforts'. Actually holding territory was contingent on the lord and his comitavae, essentially a private warband. These could be made up of vassals, relatives, tenants, friends and the like, and also drew a vast number of 'adventurers' - either younger sons of minor houses or wealthier 'Freemen' - and mercenaries. Some of these warbands were large enough to almost be armies. Orderic Vitalis recounts that Earl Hugh of Chester moved through Wales with an 'army rather than a household', and that the generosity of William fitz Osbern of Hereford attracted so many followers that William I even became concerned at his potential power.

If you're indeed a 'minor knight' then it's most likely that your bequest is a direct result of your involvement in the warband of your friend in a high place. If you're lucky, that friend may dedicate further resources to you; Robert of Rhuddlan and William fitz Osbern were both known for their generosity to their followers as much as for their ruthless persecution of the Welsh. Robert fitz Stephen's expedition to Ireland in 1169, chronicled by his nephew Gerald of Wales, was in part financed by the merchants of Bristol, and his force of 30 knights contained many of his own relatives and retainers who would then be set up with estates in Ireland.

Actually transforming your claim into tangible control was a long task. Your first task in attracting a population would be the construction of a castle to offer protection and stability, especially in a turbulent frontier area. This would allow you and your small band of retainers to establish control over a relatively large area. The castle needn't be large: the Welsh Marches are studded with many, many small 'pillbox' castles. These would not only provide immediate safety and a base of operations, but in combination with the other small castles of the other minor nobles established nearby, would project control over a wide area. Simply the presence of a castle would often be enough to encourage the rapid development of a small borough under its walls. Cardiff, Rhuddlan, Brecon are all notable examples, although the pattern was common across Wales. The colonists who established these settlements might already be part of your retinue: tenants who've agreed to accompany you, enterprising freemen, or household retainers. Some, if not most, are likely to have been younger sons or junior relatives who did not stand to take over significant holdings in their home villages and who hoped for more extensive prospects in new lands. As a whole, these colonists would stand to hold the same rights and responsibilities as they held elsewhere, although you may wish to have taken a leaf from William fitz Osbern's book and offered more generous land holdings or more lenient taxation in order to attract more colonists.

I always recommend R.R. Davies The Age of Conquest: Wales, 1063 - 1415.