When you buy an electric bass, you will necessarily need to also get an amplifier for two reasons: the electric bass does not have a soundbox so you will hear almost nothing of what you play, the other reason - which is linked to the first - is that, hearing little of what you play, you won't get the right feedback of your amplified sound. The amplifier will serve to give you the real effect of your sound as it will be within a band, it will allow you to hear the nuances better, if the instrument is too sharp or if your approach is not correct.
There are various types of amplifiers: the combo combines in a single instrument the head, that is, the amplifier itself, with the cabinet, and this is one of the most practical choices for starting and not only. The market offers a wide range of choices proposing combos from a few watts, ideal for home study to very manageable ones, and others that exceed 300 watts, excellent also for live concerts.
Furthermore, other features concern the type of head that can be valve, transistor, or digital and the diameter of the cone of the speaker. Each of these features will determine the type of sound output and also your choices, without neglecting the differences in weight between the various models, and the weight often ends up influencing your choices as well.