I have my site on dedicated Apache/Linux server now. Is NginX something I install on there or is it a server? If it is a server where do I find then to host my site? What do I look for?
Its a replacement for apache basically. It is in fact quite a bit faster as well. I have been meaning to switch over to it myself but I have been too busy to futz with it. Nigel
It's more than just a webserver; it can also serve as a load balancer and front-end proxy. There are a ton of extensions that can be loaded as well to give it more functionality. It functions quite differently than Apache and at first the configuration format is odd but once you grok it you'll love it's performance and flexibility.
If you have the opportunity to switch to it over Apache, do it. We use it here for our web server as well as php-fpm load balancing. It's nice because it supports SPDY right out of the box (Apache requires much more effort to make SPDY work).
nginx is a web server (same like apache) with some advantages over apache as it's lighter. you can go to nginx.org for more information
I almost exclusively use NGINX now. It's so fast, easy to use and yeah, it supports SPDY out of the box and I think they recently (like 5 days ago) upgraded the implementation.
So at all you'd prefer nginx especially if you're about setting up a server newly? Wats about security aspects? Apache 2.4.7 offers a lot of modules for such. My question to you is: I'm going to run a server on which approx. 20 sites will be hosted with 50k total hits per day. Should I use NGINX or apache (if I'm not going to expand)?
it depends on what those sites need, are they using complex rewrite rules? because if they are, you'll need to translate from apache's rewrite rules to nginx's rewrite rules. some popular CMS such wordpress already have nginx rewrite rules but if you use custom scripts for example then you have to write the rules your self
if You use low budget VPS, i think NGINX is a good choice. about rewrite rule, there are many tutorial or You can ask at forums.