GMRS is allocated 30 frequency channels in the range of 462 MHz to 467 MHz, which are divided into 22 simplex channels (where you transmit and receive directly) and 8 repeater channels (where you transmit to a repeater, which receives and re-transmits your signal on a different channel).
Generally, when setting up a frequency channel on a radio, we transmit and receive signals on the same frequency. However, for GMRS repeater channels, we set up transmit and receive frequencies differently; the difference between these two frequencies is usually 5 MHz. In some cases, such as yours, these frequencies may already be pre-set.
However, most repeaters require that you transmit a specific tone (often called PL, CTCSS, QC or CG) before they listen to your transmission. Therefore, you may need to set the tone value for the repeater channel you want to use.