Stock music is able to make your medium truly impressive. Music is able to change everything and make a video or a game a lot more pleasant, since music is used to create the necessary mood and it is very effective. Try to remember a horror film you have seen. Try to remember music from the film. Music was used to enhance the visual part of the film. Quite often the music is quite calm and then it is changed to a dramatic track together with fast changing of visual part (like appearing of a monster). Music creates the necessary atmosphere.
Sound effects should not be underestimated as well. Try to watch a horror film without sound and the scary effect will disappear.
Music has to be used properly. There are many ways to use music tracks which you can find at http://allstockmusic.com/. You can use the music tracks in your video, game, film, etc. You can go even further and create your own remix combining several tracks into one impressive piece.
Audio editing tools
Sometimes you may need to modify a track and add a special touch to it. For example, you have 2 min video and you want to add a background music track to it. In this case, you need to extract a 2 min long piece from the track. Alternatively, you may want to add a special filter to get the right sound. Luckily, there are many wonderful programs, which are easy to use.
It is a very popular audio editing tool from Adobe. It supports many file formats and offer you a wide range of tools and effects to get the right sound. The last version is available via the subscription, so you will not have to spend too much.
This program is used be professionals all over the world. It is extremely powerful, but it is still quite complex and it is hard to use it, especially if you are new to audio editing. However, it has many useful functions and features. This software is quite expensive ($159).
Audacity is free and it includes many useful features, like VST and LADSPA effects. This is a perfect option if you do not need any complex audio editing.