Gain: This control adjusts the amount of signal that is sent from your bass guitar to the preamplifier section of the amp. Increasing the gain will make your bass sound louder and more distorted, while decreasing the gain will make it sound quieter and cleaner.
EQ: The EQ section of a bass amp allows you to adjust the frequency response of the sound. This is typically done with a three-band EQ, which includes controls for bass, mid, and treble. Boosting the bass will make your sound more boomy and low-end heavy, while boosting the mid will make it louder and more present. Boosting the treble will make your sound brighter and more high-end heavy.
Volume: This control adjusts the overall output volume of the amp.
Master: The master control is used to set the overall balance between the preamplifier and power amplifier sections of the amp.
Input: This is where you plug your bass guitar into the amp.
Output: This is where you connect the amp to a speaker cabinet.
Effects loop: An effects loop is a feature on some amps that allows you to connect external effects pedals between the preamplifier and power amplifier sections of the amp. This can be useful for adding effects such as reverb, delay, and distortion to your bass sound.