Sometimes in large venues where a professional PA system and sound man are present, the bass player can just plug into the PA system and hear himself through monitors.  However, for smaller venues or for large venues with a system that does not have excellent, powerful monitors, all bass players who are performing in public need either an amp and a speaker cabinet, or a "combo amp" that has the amp and speaker cabinet in one unit.  Good bass amps with enough power for performing in loud bands in large venues are expensive, and speaker cabinets big enough to create massive bottom end tone are large and heavy.  It is common to spend more on the amp and cabinet than on the bass itself.

Fortunately, there is no need for a beginner student to spend that kind of money.  Several less expensive alternatives are available.

For learning and practicing, one of the easiest options is if you have a decent sound system on your computer with a subwoofer, just plug the bass into your computer.  This way, you can play along with mp3’s and YouTube videos.  You’ll need a 10-15' 1/4” male mono (TS) to 1/8” male mono (TS) cord to plug into the bass on one end and the computer microphone input jack on the other.  (Or a regular guitar cord plus a short 1/4" female to 1/8" male adapter.  For a newer Mac that has no headphone jack, you'll need a lightning or USB-C adapter.)  You'll also need software that allows the sound from the microphone input to go directly to the speakers.  (For Mac, this can be done with the Garage Band app.  I’m not sure for Windows.)

Another option for in-home use is a small, inexpensive PA speaker with a bluetooth input and a 1/4" "Mic" input jack, such as the Ion Tailgater Plus that is priced dirt cheap (about $100 at Sam's Club).  These don't make a lot of noise, but the tone is great.

Another option is to buy a larger powered PA loudspeaker that can be used both for practice and for gigging.  And later, when you decide to buy a better bass amp, this one can be used in your PA system.  For example, the ION Total PA Max (below) has a 2 channel mixer, a 500 Watt amplifier, a 15" woofer, and a horn tweeter for about $225 (sometimes Sam's Club puts them on sale for even less).  This speaker is not made specifically for bass guitar, but it sounds surprisingly good for the price, and it is quite loud.  It even has bluetooth so you can play songs from your phone into it and play along with them. 

If you want a combo amp specifically made for bass guitar, you get the most for your money in the lower price ranges with the Fender Rumble series.  For example, for $300 you can get a 100 Watt bass combo (below) with a 12" Eminence speaker, that has tube amp overdrive emulation and a good variety of tone choices.  There are smaller ones in the Rumble series for less money and larger ones for more.  The Book Table sells these amps locally for Internet prices.

In the higher price ranges, there are several brands that are excellent.  If this is the route you want to take, I recommend that you take your bass to Guitar Center and play through a bunch of them until you find one you like for a price you can afford.  I personally use a TC Electronic RH750 amp with an SWR 4x10 cabinet, but there are a lot of other good choices out there.

NOTE: I do not recommend playing bass through an electric guitar amp.  The bass will sound terrible, and if you turn it up loudly the bass frequencies can blow the speaker.