Translation:You give a new computer to Sebastian.
The computer is given to Sebastian. In English we can use an indirect object, "You give Sebastian a new computer" (more common), or we can use "to", "You give a new computer to Sebastian".
The equivalent in Romanian (and also certain other languages, like Latin and Polish) is to use the dative case of the noun. With most names this is done by preceding the name with "lui". It's the same as with the genitive - "Calculatorul lui Sebastian" - Sebastian's computer.