There are varying adapters available that you can use on the Pi:
- HDMI → DVI
- DVI → VGA
- HMDI → VGA
- composite → VGA
- composite → SCART
You can get a list of verified peripherals here - these include and recommends externally powered adapters, but also includes some (cheaper) non-powered ones, as explained (this may concern only the old Pi models):
Note that active converter boxes may draw power through the HDMI port,
and thus will put an extra load on your PSU, and also increase the
current running through the Raspberry Pi's primary input fuse. HDMI
ports (and the raspberry PI) are designed so that they deliver a very
limited amount of power (50 mA) to the TV/Monitor/display-adapter and
much more isn't in theory allowed. In fact there is a diode (D1) in
series with the power line which can only handle 200 mA, if the
adapter tries to draw much more than that the diode might fail.
Therefore only externally powered adapters are to be recommended.
Despite this, many people report success with non externally powered
devices. If you have bought a non externally powered HDMI to VGA
adapter, and you experience problems with it (It behaves badly, D1
burns out, F3 "blows", or your PSU overloads), then not all is lost,
there are cheap (a few dollars) adapters that allow you to add
external power to the HDMI cable! An example can be found here: [13]
The HDMI adapters require power (here (from here) shows pin 18 needs +5 V (min. 0.055 A)), which usually should give 0.55A whilst adapters may need more power (VGA spec apparently does not specify).
This is why the page shows that you can use this, though it does show you can use a few non-powered converters work here.
You can also use the composite video output (read here for newer versions), another alternative is to use a RDP or VNC server and a remote desktop client on another machine on the network to view what is on the Pis screen.