Should I download a video codec?

if you want to watch the video you'll need the codec.

otherwise get another media player (which may still need to download the codec).

http://www.videolan.org/vlc/ my favourite media player.

Watch out! What you normally need only is Adobe Flash Player to watch videos online. Make sure you get that one first:

http://get.adobe.com/flashplayer/otherversions/

If the website still requires you to install a video codec then that sounds fishy.

As you don't know much about security, I suggest that you take these precautionary measures:

1. Use a secure browser like Firefox:

http://www.filehippo.com/download_firefox/

2. Add Web of Trust add-on

http://www.mywot.com/

3. Use a decent anti-virus and anti-spyware:

http://www.avast.com/free-antivirus-download

http://www.malwarebytes.org/products/malwarebytes_...

Try the 14-day full version of Malwarebytes. It would be best if you can get the lifetime license for only $25. That'll protect you from malicious websites that try to trick you to install fake programs.

4. If you want to know if a site is safe or not, you may use any of these to guide you:

https://www.mywot.com/

http://safeweb.norton.com/

http://www.siteadvisor.com/

You can download one of the latest version of K-lite, a collection of useful codecs to play all your videos/audios properly. Free Link here http://j.mp/1kl9yDs