There are plenty of audio interfaces on the market, from small and easy-to-use cheap ones to very expensive ones with a lot of technical features. Even the cheap ones can result in very good sound quality, so you don’t need to buy the most expensive one to make a really good recording.
To record audio (e.g. vocals, acoustic instruments):
Behringer U-phoria UM2 is a simple, affordable audio interface with mic and instrument inputs, costs around $30. Other options include the Focusrite Scarlett Solo, the PreSonus Audio Box and the Tascam US-2X2, all of which retail at around $100. All of these audio interfaces work with Mac/PC/Chromebook.
There are also USB mics on the market. With these kind of microphones you don’t need an audio interface to connect to your computer, you just plug in the USB cable from the mic and record!
For Mac/PC/Chromebook users, there's the Behringer C1U which retails at around $60, and the Rode NT-USB for around $170. For Mac/iOS/Chromebook users, there's the Apogee MiC for around $230. There is also a Mac/Windows 10 version of the Apogee MiC for $200.
To record external instruments:
Apogee Jam is a simple interface for Mac/iOS/Chromebook users to record electric guitar or bass. You plug the guitar into the device and then connect it to the computer USB port. It costs around $100, same as the iRig HD 2, which also works on PC computers. For Mac/PC/Chromebook users, the Behringer UCG102 goes for a bit less at around $40.
Remember that you will also need an instrument cable to connect your instrument to the interface.
Of course there are many other good interfaces on the market and the ones mentioned here are just examples!