You can either use a "Y" and run the ailerons off a single channel, or plug each aileron servo into its own channel (usually channel 1 and channel 6). The advantage of using separate channels is easier setup. When using a "Y" the subtrim function from your transmitter will impact both ailerons. With each aileron on a separate channel you can set the subtrim for each individually, allowing you to center each aileron independent of the other. In theory if your pushrods are setup correctly you can accomplish the same thing mechanically by screwing the clevis in or out on the rod as needed. However, this process is subject to two issues. First, you are limited to half turn adjustments of the clevis. Second, you are also limited by the splines on the servo, which must align to the servo arm mount. It is almost never the case that this will allow for exact centering of both servos, nor is it likely that both will be "off" by the exact same amount. If they are run on a single channel the subtrim will, of course, impact both of them, but if each is on its own channel each can be centered independently.