Printer

What they do
They allow you to print in back and white or colour both text and images.
 
Quality to consider before purchasing one
The main things to consider in an inkjet printer are: printing quality, reliability over time, cost and duration of cartridges (which in certain cases can cost as much as the printer itself!)

Printing quality is what is most easily visible; if you want a photographic quality (that is the printed image is identical to the image displayed on your monitor), you have to buy a printer with 6 colours, given that the printers with four colours can only achieve reasonable results but never excellent results.

Reliability is very important, especially if you are planning to print a lot: a robust printer can easily print thousands and thousands of pages without giving you any problems. A cheap printer will manifest its shortcomings after a little while.

It may also be useful to buy a printer with Auto Duplexing for double sided printing (in general HP models) so that pages are automatically printed on both sides.

Cartridges have become a real issue: in many cases a cartridge costs as much as the printer itself. Before purchasing a printer, it is essential to check the type of cartridges that it uses, how much the latter cost, how much ink they contain and whether the printer uses up a lot of ink (for instance, Epson printers use much more ink than HP). If you are considering buying rechargeable cartridges, remember that Epson printers have fixed heads and that as a consequence a low quality ink may obstruct them and permanently damage the printing quality.
The cost of a good quality A4 printer is about 100 USD. For a printer with photographic quality, you have to double that price.
Brands to keep in mind (Printer sale)

1) HP (reliable, heads inserted in the cartridge so that when you change the cartridge, the quality of printing becomes as good as new).
2) Epson (excellent printing quality, use up a lot of ink)
3) Canon