Programatically set permissions to the SharePoint Site

SPSite spSite= null;
SPWeb spWeb = null;

using(spSite = new SPSite("SiteUrl")
{
spWeb= spSite.OpenWeb();
spWeb.AllowUnSafeUpdates = true;
SPRoleAssignment spRoleAssignment = new SPRoleAssignment ("domain\\UserName","alias@domain.com","UserName","Test Message");
SPRoleDefinition spRoleDefinition = spWeb.RoleDefinitions.GetByType(SPRoleType.
Administrator);
spRoleAssignment.RoleDefinitionBindings.Add(spRoleDefinition);
spWeb.RoleAssignments.Add(spRoleAssignment);
spWeb.Dispose();
spWeb.AllowUnSafeUpdates = false;
}