Is there a site or a software from which you can download or create sound effects like bullets and crashing of glass?
audacity can’t create different sound effects. It can only edit audio,
Audacity You can change the Pitch and Speed to create the dramatic effect with the original sound.
This Video http://www.youtube.com/watch?v=yPSzOo4Bml4
and This video
http://www.youtube.com/watch?v=OIivAp7Xk-g
Previous Video Sound and in the next video sound telling End of the World with you same sound changed with audacity
FL studio has a free trial that allows exporting. What you are looking for is a DAW (Digital Audio Workstation) And the free one I know about is called LMMS.
But like I said you can use FL Studio for free to, just can’t save your project for future editing.
Soundsnap.com, is the definitive source for sound effects imo. For $100.00 you can get a decent USB Mic, find a nice room with good acoustics, and start doing some of your own Foley. It’s really fun and rewarding.
Audacity can generate a handful of simple sounds, which can then be tweaked.
I assume there are probably syth plugins you can add to generate more custom sounds. Not an expert, so just guessing.
hey 3dementia, if you use LMMS, i have a question I have just downloaded LMMS and i am struggling to understand it. When i open the piano roll editor, it says in big green letter that i have to double click a pattern. How do i do that? I dont understand ? If you look at a tutorial at the Wiki named My first song, it says somewhere that open the Moog track or something and Open the Piano Roll Editor. What does that supposed to mean?
Just make the sound effects yourself.
“I got two turn-tables and a microphone…”
Uncountable sites with stuff from weapon lovers, some with several variations for every standard weapon
or ammo, recorded from various distances, too much to post them all,
for instance feed the search bot of your choice with: “rd_gunsound_v1.0.zip.zip”
btw finding some nice, very short and ready to use combat sounds for my Wiz8 mod (Fantasy RPG)
appears somewhat harder, so i also use audacity to edit sounds,
as its somewhat slow in creating large mp3`s, i recommend “export multiple” in background.
with with the rather common function “sound_triggered_automatic_recording” even that isnt required 
Audacity is excellent, but has a steep learning curve and is very hard to use without a starting point. (i.e. a sound effect you recorded.)
I recommend WavePad. It comes with a built in sound library and has a very simple, yet effective toolbox and interface. It also helps to understand sound wave theory when using such programs. you can learn sound theory in like 10 minutes, just youtube it.
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There are many of free VST what you could use to create even complex sound effects.
Look here, for example: http://freemusicsoftware.org/category/free-vst/sound-fx