Aegisub does not depend on any external codecs, it uses a built-in ffmpeg version on Windows and Mac. On Linux and BSD systems it will typically use the system ffmpeg installation.
On Windows, you are able to use Avisynth to load unusual video and audio formats, and use system codecs through that, but it's optional and very uncommon.
There are no particular system requirements for Aegisub above those for the base operating system, other than requiring a graphics card with OpenGL support; all current Intel, NVidia and AMD graphics chipsets support that.
Screen resolution should be at least 1024x768. Dual monitors can be supported by using the "detached video" feature.
Windows versions supported are Windows Vista, 7, 8, 8.1 and 10, possibly also Windows XP SP3 but I wouldn't recommend that.
Do not PM me asking for help with Aegisub, Automation, karaoke or anything like that, I won't reply.
Ask your questions in the public forums. Use the Search function, somebody probably asked the same question before.
All rights reserved to call you insults if you ask poorly thought out or redundant questions.
Experimenting is free and is a great way to learn things.