Tuning
VFO lets you set mode, receive and transmit frequency (with repeater-offset shortcuts), power, bandwidth and tones, or colour code, slot and call target for DMR, without saving a channel.
Frequency range
The radio tunes 136–174 MHz and 400–480 MHz only; it refuses anything else (220 MHz included) and stays where it was, so the app never sends it. If the radio does refuse a channel (for example a DMR channel without a call number), the history says so and the display goes back to the frequency the radio is really on.
While VFO is on
The arrows step the frequency by the step you chose and the big number reads VFO. Long-press VFO to return to your channel. Save as channel keeps a frequency you want to come back to.
Band plan
Under the frequencies, the VFO and the channel editor say what each one is used for: the US amateur band plan for 2 m and 70 cm (repeater inputs and outputs, simplex and calling frequencies, satellites, weak signal, APRS) and the other services in this radio's range (FRS and GMRS, MURS, marine, railroad, NOAA, land mobile, government). It turns amber with a caution where transmitting needs another licence, is not allowed or would disturb a special use. Amateur plans are the typical ARRL ones; your area's coordinator may differ.