When an AP is in bridging mode it effectively forwards frames received on one interface and out of the other thus bridging the 2 interfaces. Typically you would use this to connect disparate parts of your building not serviceable by cable or fibre.
A wireless repeater or extender is different, it will pick up and regenerate the signal extending the range of an existing network.
Using either will extend the range of your network but you do need to take into consideration things like walls!!