Below, both the reactant and the product of the SN2 reaction described on the previous page are shown:
Rotate the structures to determine whether their specification is R or S, and check your findings:
As we noted on the previous page, the SN2 reaction of 2-bromooctane with OH- proceeds with inversion of configuration: the OH-group has not taken the position previously occupied by Br; rather, the attack of the OH- starts from the back-side of the molecule and leads to an inversion of the configuration of the molecule. This inversion of configuration happens in all SN2 reactions.
However, inversion of configuration is not neccessarily accompanied by a change in specification (from R to S or from S to R): the new substituent could change the Cahn-Ingold-Prelog sequence of the entire molecule.
An important remark about the SN2 reaction is that it occurs in a single step: bond-breaking and bond-making occur simultaneously, in a concerted fashion. If the reaction wouldn't be concerted, there would be no reason for it to proceed stereospecifically, as you can see in the part about the SN1 reaction.