Access Point is the main device for you to get connected.
Repeater is a device to 'bounce' the signal from your Access Point... in the purpose to extend the wireless range.
There are a Repeater that can also act as an Access Point (or vice versa - An access point that can also act as a Repeater--).
Which one is more effective?
Logically, a dedicated Access point is better than a repeater that acting as an access point.
look at www.linksys.com or www.dlink.com for product info.
how does a wireless access point and repeater differ and which is the more effective?