Coming from Barajas by airport bus. Need to move efficiently to AVE side for train to Malaga as may have only a short time to catch train. We have tickets and seat reservations in hand. Where do we check in? Do we need to pass security? Do we go first to the upper level or start on ground level. We would appreciate any advice as we don't want to wander aimlessly and the station and posts about it make it seem complicated for older travelers.